Organometallic complex, light-emitting element, light-emitting device, electronic device, and lighting device

ABSTRACT

A novel organometallic complex which can emit phosphorescence is provided. A light-emitting element, a light-emitting device, an electronic device, or a lighting device with high emission efficiency is provided. The organometallic complex having an aryl triazine derivative as a ligand is represented by General Formula (G1) below as a representative of the organometallic complex of the present invention.

TECHNICAL FIELD

One embodiment of the present invention relates to an organometalliccomplex. In particular, one embodiment of the present invention relatesto an organometallic complex that is capable of converting tripletexcited energy into luminescence. In addition, one embodiment of thepresent invention relates to a light-emitting element, a light-emittingdevice, an electronic device, and a lighting device each using anorganometallic complex.

BACKGROUND ART

Organic compounds are brought into an excited state by the absorption oflight. Through this excited state, various reactions (photochemicalreactions) are caused in some cases, or luminescence is generated insome cases. Therefore, the organic compounds have a wide range ofapplications.

As one example of the photochemical reactions, a reaction of singletoxygen with an unsaturated organic molecule (oxygen addition) is known(refer to Non-Patent Document 1). Since the ground state of an oxygenmolecule is a triplet state, oxygen in a singlet state (singlet oxygen)is not generated by direct photoexcitation. However, in the presence ofanother triplet excited molecule, singlet oxygen is generated to causean oxygen addition reaction. In this case, a compound capable of formingthe triplet excited molecule is referred to as a photosensitizer.

As described above, for generation of singlet oxygen, a photosensitizercapable of forming a triplet excited molecule by photoexcitation isneeded. However, the ground state of an ordinary organic compound is asinglet state; therefore, photoexcitation to a triplet excited state isforbidden transition and generation of a triplet excited molecule isdifficult. A compound that can easily cause intersystem crossing fromthe singlet excited state to the triplet excited state (or a compoundthat allows the forbidden transition of photoexcitation directly to thetriplet excited state) is thus required as such a photosensitizer. Inother words, such a compound can be used as the photosensitizer and isuseful.

The above compound often exhibits phosphorescence. Phosphorescencerefers to luminescence generated by transition between differentenergies in multiplicity. In an ordinary organic compound,phosphorescence refers to luminescence generated in returning from thetriplet excited state to the singlet ground state (in contrast,fluorescence refers to luminescence in returning from the singletexcited state to the singlet ground state). Application fields of acompound capable of exhibiting phosphorescence, that is, a compoundcapable of converting the triplet excited state into luminescence(hereinafter, referred to as a phosphorescent compound), include alight-emitting element including an organic compound as a light-emittingsubstance.

This light-emitting element has a simple structure in which alight-emitting layer including an organic compound that is alight-emitting substance is provided between electrodes. Thislight-emitting element attracts attention as a next-generation flatpanel display element in terms of characteristics such as being thin andlight in weight, high speed response, and direct current low voltagedriving. Further, a display device including this light-emitting elementis superior in contrast, image quality, and wide viewing angle.

The light-emitting element including an organic compound as alight-emitting substance has a light emission mechanism that is of acarrier injection type: voltage is applied between electrodes where alight-emitting layer is interposed, electrons and holes injected fromthe electrodes are recombined to make the light-emitting substanceexcited, and then light is emitted in returning from the excited stateto the ground state. As in the case of photoexcitation described above,types of the excited state include a singlet excited state (S*) and atriplet excited state (T*). The statistical generation ratio thereof inthe light-emitting element is considered to be S*:T*=1:3.

At room temperature, a compound capable of converting a singlet excitedstate into luminescence (hereinafter, referred to as a fluorescentcompound) exhibits only luminescence from the singlet excited state(fluorescence), not luminescence from the triplet excited state(phosphorescence). Accordingly, the internal quantum efficiency (theratio of the number of generated photons to the number of injectedcarriers) of a light-emitting element including the fluorescent compoundis assumed to have a theoretical limit of 25%, on the basis ofS*:T*=1:3.

On the other hand, in a case of a light-emitting element including thephosphorescent compound described above, the internal quantum efficiencythereof can be improved to 75% to 100% in theory; namely, the emissionefficiency thereof can be 3 to 4 times as much as that of thelight-emitting element including a fluorescent compound. Therefore, thelight-emitting element including a phosphorescent compound has beenactively developed in recent years in order to achieve ahighly-efficient light-emitting element (refer to Non-Patent Document2). An organometallic complex that contains iridium or the like as acentral metal is particularly attracting attention as a phosphorescentcompound because of its high phosphorescence quantum yield.

REFERENCE Non-Patent Document

[Non-Patent Document 1]

Inoue, Haruo, and three others, Basic Chemistry Course PHOTOCHEMISTRY I,pp. 106-110, Maruzen Co., Ltd.

[Non-Patent Document 2]

Zhang, Guo-Lin, and five others, Gaodeng Xuexiao Huaxue Xuebao (2004),vol. 25, No. 3, pp. 397-400.

DISCLOSURE OF INVENTION

It is an object of one embodiment of the present invention to provide anovel organometallic complex capable of emitting phosphorescence. It isanother object of one embodiment of the present invention to provide alight-emitting element, a light-emitting device, an electronic device,or a lighting device with high emission efficiency. Further, it is stillanother object of one embodiment of the present invention to provide alight-emitting element with low power consumption.

One embodiment of the present invention is an organometallic complex inwhich an aryl triazine derivative is a ligand. Therefore, one embodimentof the present invention is an organometallic complex having a structurerepresented by General Formula (G1) below.

In the formula, R¹ represents any of a substituted or unsubstitutedalkyl group having 1 to 4 carbon atoms, a substituted or unsubstitutedmonocyclic saturated hydrocarbon having 5 to 7 carbon atoms, asubstituted or unsubstituted polycyclic saturated hydrocarbon having 7to 10 carbon atoms, and a substituted or unsubstituted aryl group having6 to 10 carbon atoms, R² represents hydrogen or a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, and Ar¹ representsa substituted or unsubstituted arylene group having 6 to 10 carbonatoms. M represents a Group 9 element or a Group 10 element.

Another embodiment of the present invention is an organometallic complexhaving a structure represented by General Formula (G2) below.

In the formula, R¹ represents any of a substituted or unsubstitutedalkyl group having 1 to 4 carbon atoms, a substituted or unsubstitutedmonocyclic saturated hydrocarbon having 5 to 7 carbon atoms, asubstituted or unsubstituted polycyclic saturated hydrocarbon having 7to 10 carbon atoms, and a substituted or unsubstituted aryl group having6 to 10 carbon atoms, R² represents hydrogen or a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, and R³ to R⁶separately represent any of hydrogen, a substituted or unsubstitutedalkyl group having 1 to 4 carbon atoms, a substituted or unsubstitutedalkoxy group having 1 to 4 carbon atoms, a substituted or unsubstitutedalkylthio group having 1 to 4 carbon atoms, a halogen group, asubstituted or unsubstituted haloalkyl group having 1 to 4 carbon atoms,and a substituted or unsubstituted aryl group having 6 to 10 carbonatoms. M represents a Group 9 element or a Group 10 element.

Note that an organometallic complex having the structure represented byGeneral Formula (G1) or (G2) can emit phosphorescence and thus can beadvantageously applied to a light-emitting layer of a light-emittingelement. Accordingly, a preferable mode of the present invention is aphosphorescent organometallic complex having the structure representedby General Formula (G1) or (G2). In particular, an organometalliccomplex having the structure which is represented by General Formula(G1) or (G2) and in which the lowest triplet excited state is formed inthe structure is preferable because the organometallic complex canefficiently exhibit phosphorescence.

Another embodiment of the present invention is an organometallic complexrepresented by General Formula (G3) below.

In the formula, L represents a monoanionic ligand. R¹ represents any ofa substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, asubstituted or unsubstituted monocyclic saturated hydrocarbon having 5to 7 carbon atoms, a substituted or unsubstituted polycyclic saturatedhydrocarbon having 7 to 10 carbon atoms, and a substituted orunsubstituted aryl group having 6 to 10 carbon atoms, R² representshydrogen or a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, and Ar¹ represents a substituted or unsubstituted arylenegroup having 6 to 10 carbon atoms. M represents a Group 9 element or aGroup 10 element. Moreover, n is 2 when M is a Group 9 element, and n is1 when M is a Group 10 element.

Another embodiment of the present invention is an organometallic complexrepresented by General Formula (G4) below.

In the formula, L represents a monoanionic ligand. Further, R¹represents any of a substituted or unsubstituted alkyl group having 1 to4 carbon atoms, a substituted or unsubstituted monocyclic saturatedhydrocarbon having 5 to 7 carbon atoms, a substituted or unsubstitutedpolycyclic saturated hydrocarbon having 7 to 10 carbon atoms, and asubstituted or unsubstituted aryl group having 6 to 10 carbon atoms, R²represents hydrogen or a substituted or unsubstituted alkyl group having1 to 4 carbon atoms, and R³ to R⁶ separately represent any of hydrogen,a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, asubstituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, asubstituted or unsubstituted alkylthio group having 1 to 4 carbon atoms,a halogen group, a substituted or unsubstituted haloalkyl group having 1to 4 carbon atoms, and a substituted or unsubstituted aryl group having6 to 10 carbon atoms. M represents a Group 9 element or a Group 10element. Moreover, n is 2 when M is a Group 9 element, and n is 1 when Mis a Group 10 element.

In the organometallic complex represented by General Formula (G3) or(G4), the monoanionic ligand is preferably any of a monoanionicbidentate chelate ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, a monoanionicbidentate chelate ligand having a phenolic hydroxyl group, and amonoanionic bidentate chelate ligand in which two ligand elements areboth nitrogen. A monoanionic bidentate chelate ligand having abeta-diketone structure is particularly preferable.

Note that the monoanionic ligand is preferably a ligand represented byany of General Formulae (L1) to (L7) below.

In General Formulae (L1) to (L7), R¹¹ to R⁴⁸ separately represent any ofhydrogen, a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, a halogen group, a vinyl group, a substituted orunsubstituted haloalkyl group having 1 to 4 carbon atoms, a substitutedor unsubstituted alkoxy group having 1 to 4 carbon atoms, and asubstituted or unsubstituted alkylthio group having 1 to 4 carbon atoms.Further, A¹ to A³ separately represent any of nitrogen, sp² hybridizedcarbon bonded to hydrogen, and sp² hybridized carbon bonded to any of analkyl group having 1 to 4 carbon atoms, a halogen group, a haloalkylgroup having 1 to 4 carbon atoms, and a phenyl group.

Another embodiment of the present invention is an organometallic complexrepresented by General Formula (G5) below.

In the formula, R¹ represents any of a substituted or unsubstitutedalkyl group having 1 to 4 carbon atoms, a substituted or unsubstitutedmonocyclic saturated hydrocarbon having 5 to 7 carbon atoms, asubstituted or unsubstituted polycyclic saturated hydrocarbon having 7to 10 carbon atoms, and a substituted or unsubstituted aryl group having6 to 10 carbon atoms, R² represents hydrogen or a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, and Ar¹ representsa substituted or unsubstituted arylene group having 6 to 10 carbonatoms. M represents a Group 9 element or a Group 10 element. Moreover, nis 3 when M is a Group 9 element, and n is 2 when M is a Group 10element.

Another embodiment of the present invention is an organometallic complexrepresented by General Formula (G6) below.

In the formula, R¹ represents any of a substituted or unsubstitutedalkyl group having 1 to 4 carbon atoms, a substituted or unsubstitutedmonocyclic saturated hydrocarbon having 5 to 7 carbon atoms, asubstituted or unsubstituted polycyclic saturated hydrocarbon having 7to 10 carbon atoms, and a substituted or unsubstituted aryl group having6 to 10 carbon atoms, R² represents hydrogen or a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, and R³ to R⁶separately represent any of hydrogen, a substituted or unsubstitutedalkyl group having 1 to 4 carbon atoms, a substituted or unsubstitutedalkoxy group having 1 to 4 carbon atoms, a substituted or unsubstitutedalkylthio group having 1 to 4 carbon atoms, a halogen group, asubstituted or unsubstituted haloalkyl group having 1 to 4 carbon atoms,and a substituted or unsubstituted aryl group having 6 to 10 carbonatoms. M represents a Group 9 element or a Group 10 element. Moreover, nis 3 when M is a Group 9 element, and n is 2 when M is a Group 10element.

Further, the organometallic complex of one embodiment of the presentinvention is very effective for the following reason: the organometalliccomplex can emit phosphorescence, that is, it can convert tripletexcitation energy into emission and can exhibit emission, and thereforehigher efficiency is possible when the organometallic complex is appliedto a light-emitting element. Thus, the present invention also includes alight-emitting element in which the organometallic complex of oneembodiment of the present invention is used.

Other embodiments of the present invention are not only a light-emittingdevice including the light-emitting element but also an electronicdevice and a lighting device each including the light-emitting device.The light-emitting device in this specification refers to an imagedisplay device, a light-emitting device, and a light source (e.g., alighting device). In addition, the light-emitting device includes, inits category, all of a module in which a light-emitting device isconnected to a connector such as a flexible printed circuit (FPC), atape automated bonding (TAB) tape or a tape carrier package (TCP), amodule in which a printed wiring board is provided on the tip of a TABtape or a TCP, and a module in which an integrated circuit (IC) isdirectly mounted on a light-emitting element by a chip on glass (COG)method.

According to one embodiment of the present invention, a novelorganometallic complex capable of emitting phosphorescence can beprovided. With the use of the novel organometallic complex, alight-emitting element, a light-emitting device, an electronic device,or a lighting device with high emission efficiency can be provided.Alternatively, it is possible to provide a light-emitting element, alight-emitting device, an electronic device, or a lighting device withhigh reliability. Further alternatively, it is possible to provide alight-emitting element, a light-emitting device, an electronic device,or a lighting device with low power consumption.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a structure of a light-emitting element;

FIG. 2 illustrates a structure of a light-emitting element;

FIGS. 3A and 3B illustrate structures of light-emitting elements;

FIG. 4 illustrates a light-emitting device;

FIGS. 5A and 5B illustrate a light-emitting device;

FIGS. 6A to 6D illustrate electronic devices;

FIG. 7 illustrates lighting devices;

FIG. 8 shows a ¹H NMR chart of an organometallic complex represented byStructural Formula (100);

FIG. 9 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of an organometallic complex represented by Structural Formula(100);

FIG. 10 illustrates a light-emitting element;

FIG. 11 shows luminance vs. current efficiency characteristics of alight-emitting element;

FIG. 12 shows voltage vs. luminance characteristics of a light-emittingelement; and

FIG. 13 shows an emission spectrum of a light-emitting element.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments and examples of the present invention will bedescribed in detail with reference to the accompanying drawings. Notethat the present invention is not limited to the description below, andmodes and details thereof can be modified in various ways withoutdeparting from the spirit and the scope of the present invention.Therefore, the present invention should not be construed as beinglimited to the description of the following embodiments and examples.

Embodiment 1

In this embodiment, organometallic complexes which are embodiments ofthe present invention will be described.

An organometallic complex that is one embodiment of the presentinvention is an organometallic complex in which an aryl triazinederivative is a ligand. Note that one mode of an organometallic complexin which an aryl triazine derivative is a ligand and which is describedin this embodiment is an organometallic complex having the structurerepresented by General Formula (G1) below.

In General Formula (G1), R¹ represents any of a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted monocyclic saturated hydrocarbon having 5 to 7 carbonatoms, a substituted or unsubstituted polycyclic saturated hydrocarbonhaving 7 to 10 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 10 carbon atoms, R² represents hydrogen or asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, andAr¹ represents a substituted or unsubstituted arylene group having 6 to10 carbon atoms. M represents a Group 9 element or a Group 10 element.

Here, specific examples of Ar¹ include a phenylene group, a phenylenegroup substituted by one or more alkyl groups each having 1 to 4 carbonatoms, a phenylene group substituted by one or more alkoxy groups eachhaving 1 to 4 carbon atoms, a phenylene group substituted by one or morealkylthio groups each having 1 to 4 carbon atoms, a phenylene groupsubstituted by one or more aryl groups each having 6 to 10 carbon atoms,a phenylene group substituted by one or more halogen groups, a phenylenegroup substituted by one or more haloalkyl groups each having 1 to 4carbon atoms, and a substituted or unsubstituted naphthalene-diyl group.

Further, specific examples of the alkyl group having 1 to 4 carbon atomsin R¹ and R² include a methyl group, an ethyl group, a propyl group, anisopropyl group, a butyl group, a sec-butyl group, an isobutyl group,and a tert-butyl group. Specific examples of the monocyclic saturatedhydrocarbon having 5 to 7 carbon atoms in R¹ and R² include acyclopentyl group, a cyclohexyl group, and a cycloheptyl group. Specificexamples of the polycyclic saturated hydrocarbon having 7 to 10 carbonatoms in R¹ and R² include a norbornyl group, a 1-adamantyl group, a2-adamantyl group, and a pinanyl group. Specific examples of the arylgroup having 6 to 10 carbon atoms in R¹ and R² include a phenyl group, aphenyl group substituted by one or more alkyl groups each having 1 to 4carbon atoms, a phenyl group substituted by one or more alkoxy groupseach having 1 to 4 carbon atoms, a phenyl group substituted by one ormore alkylthio groups each having 1 to 4 carbon atoms, a phenyl groupsubstituted by one or more aryl groups each having 6 to 10 carbon atoms,a phenyl group substituted by one or more halogen groups, a phenyl groupsubstituted by one or more haloalkyl groups each having 1 to 4 carbonatoms, and a naphthalen-yl group. Further, in terms of a heavy atomeffect, M is preferably iridium (Ir) in the case of a Group 9 elementand is preferably platinum (Pt) in the case of a Group 10 element.

Note that a substituted or unsubstituted phenylene group is preferablyused in Ar¹ above for easier synthesis. Thus, another embodiment of thepresent invention is an organometallic complex having the structurerepresented by General Formula (G2) below.

In General Formula (G2), R¹ represents any of a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted monocyclic saturated hydrocarbon having 5 to 7 carbonatoms, a substituted or unsubstituted polycyclic saturated hydrocarbonhaving 7 to 10 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 10 carbon atoms, R² represents hydrogen or asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, andR³ to R⁶ separately represent any of hydrogen, a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted alkoxy group having 1 to 4 carbon atoms, a substituted orunsubstituted alkylthio group having 1 to 4 carbon atoms, a halogengroup, a substituted or unsubstituted haloalkyl group having 1 to 4carbon atoms, and a substituted or unsubstituted aryl group having 6 to10 carbon atoms. M represents a Group 9 element or a Group 10 element.

Here, specific examples of R¹, R², and M can be the same as those of R¹,R², and M in General Formula (G1). Specific examples of R³ to R⁶separately include, hydrogen, a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, a sec-butyl group, an isobutylgroup, a tert-butyl group, a methoxy group, an ethoxy group, a propoxygroup, an isopropoxy group, a butoxy group, a sec-butoxy group, anisobutoxy group, a tert-butoxy group, a methylsulfinyl group, anethylsulfinyl group, a propylsulfinyl group, an isopropylsulfinyl group,a butylsulfinyl group, an isobutylsulfinyl group, a sec-butylsulfinylgroup, a tert-butylsulfinyl group, a fluoro group, a fluoromethyl group,a difluoromethyl group, a trifluoromethyl group, a chloromethyl group, adichloromethyl group, a trichloromethyl group, a bromomethyl group, a2,2,2-trifluoroethyl group, a 3,3,3-trifluoropropyl group, a1,1,1,3,3,3-hexafluoroisopropyl group, a phenyl group, a phenyl groupsubstituted by one or more alkyl groups each having 1 to 4 carbon atoms,a phenyl group substituted by one or more alkoxy groups each having 1 to4 carbon atoms, a phenyl, group substituted by one or more alkylthiogroups each having 1 to 4 carbon atoms, a phenyl group substituted byone or more aryl groups each having 6 to 10 carbon atoms, a phenyl groupsubstituted by one or more halogen groups, a phenyl group substituted byone or more haloalkyl groups each having 1 to 4 carbon atoms, asubstituted or unsubstituted naphthalen-yl group, and the like.

Note that an organometallic complex having the structure represented byGeneral Formula (G1) or (G2) can emit phosphorescence and thus can beadvantageously applied to a light-emitting layer of a light-emittingelement. Accordingly, a preferable mode of the present invention is aphosphorescent organometallic complex having the structure representedby General Formula (G1) or (G2).

In particular, an organometallic complex having the structure which isrepresented by General Formula (G1) or (G2) and in which the lowesttriplet excited state is formed in the structure is preferable becausethe organometallic complex can efficiently exhibit phosphorescence. Toobtain such a mode, another skeleton (another ligand) which is includedin the phosphorescent organometallic iridium complex can be selectedsuch that the lowest triplet excitation energy of the structure is equalto or lower than the lowest triplet excitation energy of the anotherskeleton (the another ligand), for example. In that case, regardless ofwhat a skeleton (ligand) other than the structure is, the lowest tripletexcited state is formed by the structure at last, so thatphosphorescence originating from the structure is thus obtained.Therefore, phosphorescence can be highly efficiently obtained. Forexample, vinyl polymer having the structure as a side chain can begiven.

One embodiment of the present invention is the organometallic complexrepresented by General Formula (G3) below.

In General Formula (G3), L represents a monoanionic ligand. R¹represents any of a substituted or unsubstituted alkyl group having 1 to4 carbon atoms, a substituted or unsubstituted monocyclic saturatedhydrocarbon having 5 to 7 carbon atoms, a substituted or unsubstitutedpolycyclic saturated hydrocarbon having 7 to 10 carbon atoms, and asubstituted or unsubstituted aryl group having 6 to 10 carbon atoms, R²represents hydrogen or a substituted or unsubstituted alkyl group having1 to 4 carbon atoms, and Ar¹ represents a substituted or unsubstitutedarylene group having 6 to 10 carbon atoms. M represents a Group 9element or a Group 10 element. Moreover, n is 2 when M is a Group 9element, and n is 1 when M is a Group 10 element. Specific examples ofAr¹, R¹, R², and M are the same as those of Ar¹, R¹, R², and M inGeneral Formula (G1).

Here, it is preferable that L that is the monoanionic ligand be any ofthe following specific examples: a monoanionic bidentate chelate ligandhaving a beta-diketone structure, a monoanionic bidentate chelate ligandhaving a carboxyl group, a monoanionic bidentate chelate ligand having aphenolic hydroxyl group, and a monoanionic bidentate chelate ligand inwhich two ligand elements are both nitrogen. A monoanionic bidentatechelate ligand having a beta-diketone structure is particularlypreferable. A beta-diketone structure is preferably included for highersolubility of an organometallic complex in an organic solvent and easierpurification. A beta-diketone structure is preferably included forrealization of an organometallic complex with high emission efficiency.Inclusion of a beta-diketone structure has advantages such as a highersublimation property and excellent evaporativity.

Specifically, L that is the monoanionic ligand is preferably a ligandrepresented by any of General Formulae (L1) to (L7) below.

In General Formulae (L1) to (L7), R¹¹ to R⁴⁸ separately represent any ofhydrogen, a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, a halogen group, a vinyl group, a substituted orunsubstituted haloalkyl group having 1 to 4 carbon atoms, a substitutedor unsubstituted alkoxy group having 1 to 4 carbon atoms, and asubstituted or unsubstituted alkylthio group having 1 to 4 carbon atoms.Further, A¹ to A³ separately represent any of nitrogen, sp² hybridizedcarbon bonded to hydrogen, and sp² hybridized carbon bonded to any of analkyl group having 1 to 4 carbon atoms, a halogen group, a haloalkylgroup having 1 to 4 carbon atoms, and a phenyl group.

Note that a phenylene group is preferably used in Ar¹ in General Formula(G3) for easier synthesis. Thus, one embodiment of the present inventionis the organometallic complex represented by General Formula (G4).

In General Formula (G4), L represents a monoanionic ligand. Further, R¹represents any of a substituted or unsubstituted alkyl group having 1 to4 carbon atoms, a substituted or unsubstituted monocyclic saturatedhydrocarbon having 5 to 7 carbon atoms, a substituted or unsubstitutedpolycyclic saturated hydrocarbon having 7 to 10 carbon atoms, and asubstituted or unsubstituted aryl group having 6 to 10 carbon atoms, R²represents hydrogen or a substituted or unsubstituted alkyl group having1 to 4 carbon atoms, and R³ to R⁶ separately represent any of hydrogen,a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, asubstituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, asubstituted or unsubstituted alkylthio group having 1 to 4 carbon atoms,a halogen group, a substituted or unsubstituted haloalkyl group having 1to 4 carbon atoms, and a substituted or unsubstituted aryl group having6 to 10 carbon atoms. M represents a Group 9 element or a Group 10element. Moreover, n is 2 when M is a Group 9 element, and n is 1 when Mis a Group 10 element. Specific examples of R¹ to R⁶ and M are the sameas those of R¹ to R⁶ and M in General Formula (G2) and specific examplesof L are the same as those of L in General Formula (G3).

Another embodiment of the present invention is the organometalliccomplex represented by General Formula (G5) below.

In General Formula (G5), R¹ represents any of a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted monocyclic saturated hydrocarbon having 5 to 7 carbonatoms, a substituted or unsubstituted polycyclic saturated hydrocarbonhaving 7 to 10 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 10 carbon atoms, R² represents hydrogen or asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, andAr¹ represents a substituted or unsubstituted arylene group having 6 to10 carbon atoms. M represents a Group 9 element or a Group 10 element.Moreover, n is 3 when M is a Group 9 element, and n is 2 when M is aGroup 10 element. Specific examples of Ar¹, R¹, R², and M are the sameas those of Ar¹, R¹, R², and M in General Formula (G1).

Another embodiment of the present invention is the organometalliccomplex represented by General Formula (G6) below.

In General Formula (G6), R¹ represents any of a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted monocyclic saturated hydrocarbon having 5 to 7 carbonatoms, a substituted or unsubstituted polycyclic saturated hydrocarbonhaving 7 to 10 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 10 carbon atoms, R² represents hydrogen or asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, andR³ to R⁶ separately represent any of hydrogen, a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted alkoxy group having 1 to 4 carbon atoms, a substituted orunsubstituted alkylthio group having 1 to 4 carbon atoms, a halogengroup, a substituted or unsubstituted haloalkyl group having 1 to 4carbon atoms, and a substituted or unsubstituted aryl group having 6 to10 carbon atoms. M represents a Group 9 element or a Group 10 element.Moreover, n is 3 when M is a Group 9 element, and n is 2 when M is aGroup 10 element. Specific examples of R¹ to R⁶ and M are the same asthose of R¹ to R⁶ and M in General Formula (G2).

Next, specific structural formulae of the above-described organometalliccomplexes each of which is one embodiment of the present invention willbe shown (Structural Formulae (100) to (142)). Note that the presentinvention is not limited to organometallic complexes represented bythese structural formulae.

Note that organometallic complexes represented by Structural Formulae(100) to (142) are novel substances capable of emitting phosphorescence.Note that there can be geometrical isomers and stereoisomers of thesesubstances depending on the type of ligand. The organometallic complexaccording to one embodiment of the present invention includes all ofthese isomers.

Next, an example of a method of synthesizing an organometallic complexhaving the structure represented by General Formula (G1) above isdescribed.

<<Method of Synthesizing Aryl Triazine Derivative Represented by GeneralFormula (G0)>>

An example of a method of synthesizing an aryl triazine derivativerepresented by General Formula (G0) below is described.

Note that in General Formula (G0), R¹ represents any of a substituted orunsubstituted, alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted monocyclic saturated hydrocarbon having 5 to 7 carbonatoms, a substituted or unsubstituted polycyclic saturated hydrocarbonhaving 7 to 10 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 10 carbon atoms, R² represents hydrogen or asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, andAr represents a substituted or unsubstituted aryl group having 6 to 10carbon atoms.

Synthesis Scheme (a) of an aryl triazine derivative represented byGeneral Formula (G0) is shown below.

Note that in Synthesis Scheme (a), to N-acylimidic acid chloride of anaryl group or an equivalent thereof (A1), amidine (A2) is added andheating is performed, so that an aryl triazine derivative (G0) isobtained. Alternatively, N-acylimidic acid chloride or an equivalentthereof and arylamidine may be reacted. Note that there are a pluralityof known methods of synthesizing the aryl triazine derivative (G0), anyof which can be employed.

Next, a synthesis method will be described of a2,4-diaryl-1,3,5-triazine derivative which is represented by GeneralFormula (G0′) below and which is an example of the aryl triazinederivative represented by General Formula (G0). In the2,4-diaryl-1,3,5-triazine derivative, R¹ in General Formula (G0) is anaryl group, and R² in Formula (G0) is hydrogen.

Synthesis Scheme (a′) of a 2,4-diaryl-1,3,5-triazine derivativerepresented by General Formula (G0′) is shown below.

Note that in Synthesis Scheme (a′), to two equivalents of amidine (A1′),one equivalent of ethyl formate or Gold's Reagent (another name:(dimethylaminomethyleneaminomethylene)dimethylammonium chloride,produced by Sigma-Aldrich Inc.) (A2′) is added and heating is performed,so that the 2,4-diaryl-1,3,5-triazine derivative (G0′) is obtained. InSynthesis Scheme (a′), Ar represents a substituted or unsubstituted arylgroup having 6 to 10 carbon atoms. Note that there are a plurality ofknown methods of synthesizing the 2,4-diaryl-1,3,5-triazine derivative(G0′), any of which can be employed.

Since the above-described compounds (A1), (A2), (A1′), and (A2′) arecommercially available as a wide variety of compounds or their synthesisis feasible, a great variety of aryl triazine derivatives can besynthesized as the aryl triazine derivative represented by GeneralFormula (G0). Thus, a feature of the organometallic complex which is oneembodiment of the present invention is the abundance of ligandvariations.

<<Method of Synthesizing Organometallic Complex of One Embodiment of thePresent Invention Represented by General Formula (G3)>>

Next, a synthesis method of the organometallic complex represented byGeneral Formula (G3) below will be described. The organometallic complexrepresented by General Formula (G3) is an example of the organometalliccomplex which is formed using the aryl triazine derivative representedby General Formula (G0) and which is one embodiment of the presentinvention.

In General Formula (G3), L represents a monoanionic ligand. R¹represents any of a substituted or unsubstituted alkyl group having 1 to4 carbon atoms, a substituted or unsubstituted monocyclic saturatedhydrocarbon having 5 to 7 carbon atoms, a substituted or unsubstitutedpolycyclic saturated hydrocarbon having 7 to 10 carbon atoms, and asubstituted or unsubstituted aryl group having 6 to 10 carbon atoms, R²represents hydrogen or a substituted or unsubstituted alkyl group having1 to 4 carbon atoms, and Ar¹ represents a substituted or unsubstitutedarylene group having 6 to 10 carbon atoms. M represents a Group 9element or a Group 10 element. Moreover, n is 2 when M is a Group 9element, and n is 1 when M is a Group 10 element. Specific examples ofAr¹, R¹, R², and M are the same as those of Ar¹, R¹, R², and M inGeneral Formula (G1).

As shown in Synthesis Scheme (b) below, the aryl triazine derivativerepresented by General Formula (G0) and a metal compound of a Group 9 orGroup 10 element which contains a halogen (e.g., rhodium chloridehydrate, palladium chloride, iridium chloride, iridium bromide, iridiumiodide, or potassium tetrachloroplatinate) are heated in an inert gasatmosphere by using no solvent, an alcohol-based solvent (e.g.,glycerol, ethylene glycol, 2-methoxyethanol, or 2-ethoxyethanol) alone,or a mixed solvent of water and one or more of the alcohol-basedsolvents, whereby a dinuclear complex (B), which is one type of anorganometallic complex including a halogen-bridged structure and is anovel substance, can be obtained.

There is no particular limitation on a heating means, and an oil bath, asand bath, or an aluminum block may be used. Alternatively, microwavescan be used as a heating means. Note that in Synthesis Scheme (b), Mrepresents a Group 9 element or a Group 10 element. Moreover, n is 2when M is a Group 9 element, and n is 1 when M is a Group 10 element.

In Synthesis Scheme (b), X represents a halogen, R¹ represents any of asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, asubstituted or unsubstituted monocyclic saturated hydrocarbon having 5to 7 carbon atoms, a substituted or unsubstituted polycyclic saturatedhydrocarbon having 7 to 10 carbon atoms, and a substituted orunsubstituted aryl group having 6 to 10 carbon atoms, R² representshydrogen or a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, and Ar represents a substituted or unsubstituted arylenegroup having 6 to 10 carbon atoms.

Furthermore, as shown in Synthesis Scheme (c) below, the dinuclearcomplex (B) obtained in Synthesis Scheme (b) above is reacted with HLwhich is a material of a monoanionic ligand in an inert gas atmosphere,whereby a proton of HL is separated and L coordinates to the centralmetal M. Thus, the organometallic complex which is one embodiment of thepresent invention represented by General Formula (G3) can be obtained.

There is no particular limitation on a heating means, and an oil bath, asand bath, or an aluminum block may be used. Alternatively, microwavescan be used as a heating means. Note that in Synthesis Scheme (c), Mrepresents a Group 9 element or a Group 10 element. Moreover, n is 2when M is a Group 9 element, and n is 1 when M is a Group 10 element.

In Synthesis Scheme (c), L represents a monoanionic ligand, X representsa halogen, R¹ represents any of a substituted or unsubstituted alkylgroup having 1 to 4 carbon atoms, a substituted or unsubstitutedmonocyclic saturated hydrocarbon having 5 to 7 carbon atoms, asubstituted or unsubstituted polycyclic saturated hydrocarbon having 7to 10 carbon atoms, and a substituted or unsubstituted aryl group having6 to 10 carbon atoms, R² represents hydrogen or a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, and Ar representsa substituted or unsubstituted arylene group having 6 to 10 carbonatoms.

Note that the monoanionic ligand L in General Formula (G3) is preferablyany of a monoanionic bidentate chelate ligand having a beta-diketonestructure, a monoanionic bidentate chelate ligand having a carboxylgroup, a monoanionic bidentate chelate ligand having a phenolic hydroxylgroup, and a monoanionic bidentate chelate ligand in which two ligandelements are both nitrogen. A monoanionic bidentate chelate ligandhaving a beta-diketone structure is particularly preferable. Abeta-diketone structure is preferably included for higher solubility ofan organometallic complex in an organic solvent and easier purification.A beta-diketone structure is preferably included for realization of anorganometallic complex with high emission efficiency. Inclusion of abeta-diketone structure has advantages such as a higher sublimationproperty and excellent evaporativity.

Further, the monoanionic ligand is preferably a ligand represented byany of General Formulae (L1) to (L7). Since these ligands have highcoordinative ability and can be obtained at low price, they are useful.

In General Formulae (L11) to (L7), R¹¹ to R⁴⁸ separately represent anyof hydrogen, a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, a halogen group, a vinyl group, a substituted orunsubstituted haloalkyl group having 1 to 4 carbon atoms, a substitutedor unsubstituted alkoxy group having 1 to 4 carbon atoms, and asubstituted or unsubstituted alkylthio group having 1 to 4 carbon atoms.Further, A¹ to A³ separately represent any of nitrogen, sp² hybridizedcarbon bonded to hydrogen, and sp² hybridized carbon bonded to any of analkyl group having 1 to 4 carbon atoms, a halogen group, a haloalkylgroup having 1 to 4 carbon atoms, and a phenyl group.

<<Method of Synthesizing Organometallic Complex of One Embodiment of thePresent Invention Represented by General Formula (G5)>>

Next, a synthesis method of the organometallic complex represented byGeneral Formula (G5) below will be described. The organometallic complexrepresented by General Formula (G5) is an example of the organometalliccomplex which is formed using the aryl triazine derivative representedby General Formula (G0) and which is one embodiment of the presentinvention.

In General Formula (G5), R¹ represents any of a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted monocyclic saturated hydrocarbon having 5 to 7 carbonatoms, a substituted or unsubstituted polycyclic saturated hydrocarbonhaving 7 to 10 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 10 carbon atoms, R² represents hydrogen or asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, andAr¹ represents a substituted or unsubstituted arylene group having 6 to10 carbon atoms. M represents a Group 9 element or a Group 10 element.Moreover, n is 3 when M is a Group 9 element, and n is 2 when M is aGroup 10 element. Specific examples of Ar¹, R¹, R², and M are the sameas those of Ar¹, R¹, R², and M in General Formula (G1).

As shown in Synthesis Scheme (d) below, the aryl triazine derivativerepresented by General Formula (G0) is mixed with a metal compound of aGroup 9 or Group 10 element which contains a halogen (e.g., rhodiumchloride hydrate, palladium chloride, iridium chloride, iridium bromide,iridium iodide, or potassium tetrachloroplatinate) or with anorganometallic complex compound of a Group 9 or Group 10 element (e.g.,an acetylacetonato complex or a diethylsulfide complex) and the mixtureis then heated, so that the organometallic complex having a structurerepresented by General Formula (G5) can be obtained.

Further, this heating process may be performed after the aryl triazinederivative represented by General Formula (G0) and the metal compound ofa Group 9 or Group 10 element which contains a halogen or theorganometallic complex compound of a Group 9 or Group 10 element aredissolved in an alcohol-based solvent (e.g., glycerol, ethylene glycol,2-methoxyethanol, or 2-ethoxyethanol). There is no particular limitationon a heating means, and an oil bath, a sand bath, or an aluminum blockmay be used. Alternatively, microwaves can be used as a heating means.Note that in Synthesis Scheme (d), M represents a Group 9 element or aGroup 10 element. Moreover, n is 3 when M is a Group 9 element, and n is2 when M is a Group 10 element.

In Synthesis Scheme (d), R¹ represents any of a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted monocyclic saturated hydrocarbon having 5 to 7 carbonatoms, a substituted or unsubstituted polycyclic saturated hydrocarbonhaving 7 to 10 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 10 carbon atoms, R² represents hydrogen or asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, andAr represents a substituted or unsubstituted arylene group having 6 to10 carbon atoms.

The above is the description of the example of a method of synthesizingan organometallic complex that is one embodiment of the presentinvention; however, the present invention is not limited thereto and anyother synthesis method may be employed.

The above-described organometallic complex that is one embodiment of thepresent invention can emit phosphorescence and thus can be used as alight-emitting material or a light-emitting substance of alight-emitting element.

With the use of the organometallic complex that is one embodiment of thepresent invention, a light-emitting element, a light-emitting device, anelectronic device, or a lighting device with high emission efficiencycan be realized. Alternatively, it is possible to realize alight-emitting element, a light-emitting device, an electronic device,or a lighting device with low power consumption.

The structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 2

In this embodiment, a light-emitting element using the organometalliccomplex in which an aryl triazine derivative is a ligand and which isdescribed in Embodiment 1 as one embodiment of the present invention isdescribed. Specifically, a light-emitting element in which theorganometallic complex is used for a light-emitting layer is describedwith reference to FIG. 1.

In a light-emitting element described in this embodiment, as illustratedin FIG. 1, an EL layer 102 including a light-emitting layer 113 isprovided between a pair of electrodes (a first electrode (anode) 101 anda second electrode (cathode) 103), and the EL layer 102 includes ahole-injection layer 111, a hole-transport layer 112, anelectron-transport layer 114, an electron-injection layer 115, acharge-generation layer (E) 116, and the like in addition to thelight-emitting layer 113.

By application of a voltage to such a light-emitting element, holesinjected from the first electrode 101 side and electrons injected fromthe second electrode 103 side recombine in the light-emitting layer 113to raise the organometallic complex to an excited state. Then, light isemitted when the organometallic complex in the excited state returns tothe ground state. Thus, the organometallic complex of one embodiment ofthe present invention functions as a light-emitting substance in thelight-emitting element.

The hole-injection layer 111 included in the EL layer 102 is a layercontaining a substance having a high hole-transport property and anacceptor substance. When electrons are extracted from the substancehaving a high hole-transport property owing to the acceptor substance,holes are generated. Thus, holes are injected from the hole-injectionlayer 111 into the light-emitting layer 113 through the hole-transportlayer 112.

The charge-generation layer (E) 116 is a layer containing a substancehaving a high hole-transport property and an acceptor substance.Electrons are extracted from the substance having a high hole-transportproperty owing to the acceptor substance, and the extracted electronsare injected from the electron-injection layer 115 having anelectron-injection property into the light-emitting layer 113 throughthe electron-transport layer 114.

A specific example in which the light-emitting element described in thisembodiment is manufactured is described.

As the first electrode (anode) 101 and the second electrode (cathode)103, a metal, an alloy, an electrically conductive compound, a mixturethereof, and the like can be used. Specifically, indium oxide-tin oxide(ITO: indium tin oxide), indium oxide-tin oxide containing silicon orsilicon oxide, indium oxide-zinc oxide (indium zinc oxide), indium oxidecontaining tungsten oxide and zinc oxide, gold (Au), platinum (Pt),nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe),cobalt (Co), copper (Cu), palladium (Pd), and titanium (Ti) can be used.In addition, an element belonging to Group 1 or Group 2 of the periodictable, for example, an alkali metal such as lithium (Li) or cesium (Cs),an alkaline earth metal such as calcium (Ca) or strontium (Sr),magnesium (Mg), an alloy containing such an element (MgAg, AlLi), a rareearth metal such as europium (Eu) or ytterbium (Yb), an alloy containingsuch an element, graphene, and the like can be used. The first electrode(anode) 101 and the second electrode (cathode) 103 can be formed by, forexample, a sputtering method, an evaporation method (including a vacuumevaporation method), or the like.

As the substance having a high hole-transport property used for thehole-injection layer 111, the hole-transport layer 112, and thecharge-generation layer (E) 116, the following can be given, forexample: aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB);3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1);3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2);3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1); and the like. In addition, the followingcarbazole derivatives and the like can be used:4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA).The substances mentioned here are mainly ones that have a hole mobilityof 10⁻⁶ cm²/Vs or higher. However, substances other than theabove-described ones may also be used as long as the substances havehigher hole-transport properties than electron-transport properties.

Further, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD) can be used.

As examples of the acceptor substance that is used for thehole-injection layer 111 and the charge-generation layer (E) 116, atransition metal oxide or an oxide of a metal belonging to any of Group4 to Group 8 of the periodic table can be given. Specifically,molybdenum oxide is particularly preferable.

The light-emitting layer 113 contains the organometallic complexdescribed in Embodiment 1 as a guest material serving as alight-emitting substance and a substance that has higher tripletexcitation energy than this organometallic complex as a host material.

Preferable examples of the substance (i.e., host material) used fordispersing any of the above-described organometallic complexes include:any of compounds having an arylamine skeleton, such as2,3-bis(4-diphenylaminophenyl)quinoxaline (abbreviation: TPAQn) and NPB,carbazole derivatives such as CBP and4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), andmetal complexes such as bis[2-(2-hydroxyphenyl)pyridinato]zinc(abbreviation: Znpp₂), bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(abbreviation: Zn(BOX)₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), and tris(8-quinolinolato)aluminum (abbreviation: Alq₃).Alternatively, a high molecular compound such as PVK can be used.

Note that in the case where the light-emitting layer 113 contains theabove-described organometallic complex (guest material) and the hostmaterial, phosphorescence with high emission efficiency can be obtainedfrom the light-emitting layer 113.

The electron-transport layer 114 is a layer containing a substancehaving a high electron-transport property. For the electron-transportlayer 114, metal complexes such as Alq₃,tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂), BAlq,Zn(BOX)₂, or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂) can be used. Alternatively, a heteroaromatic compound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: Bphen),bathocuproine (abbreviation: BCP), or4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) can beused. Further alternatively, a high molecular compound such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py), orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can be used. The substances described here aremainly ones having an electron mobility of 10⁻⁶ cm²/Vs or higher. Notethat other than these substances, any substance that has a property oftransporting more holes than electrons may be used for theelectron-transport layer.

Further, the electron-transport layer 114 is not limited to a singlelayer, and a stacked layer in which two or more layers containing any ofthe above-described substances are stacked may be used.

The electron-injection layer 115 is a layer containing a substancehaving a high electron-injection property. For the electron-injectionlayer 115, an alkali metal, an alkaline earth metal, or a compoundthereof, such as lithium fluoride (LiF), cesium fluoride (CsF), calciumfluoride (CaF₂), or lithium oxide (LiOx), can be used. Alternatively, arare earth metal compound such as erbium fluoride (ErF₃) can be used.Further alternatively, the substances for forming the electron-transportlayer 114, which are described above, can be used.

Alternatively, a composite material in which an organic compound and anelectron donor (donor) are mixed may be used for the electron-injectionlayer 115. Such a composite material is excellent in anelectron-injection property and an electron-transport property becauseelectrons are generated in the organic compound by the electron donor.In this case, the organic compound is preferably a material excellent intransporting the generated electrons. Specifically, for example, thesubstances for forming the electron-transport layer 114 (e.g., a metalcomplex and a heteroaromatic compound), which are described above, canbe used. As the electron donor, a substance showing an electron-donatingproperty with respect to the organic compound may be used. Specifically,an alkali metal, an alkaline earth metal, and a rare earth metal arepreferable, and lithium, cesium, magnesium, calcium, erbium, ytterbium,and the like are given. In addition, alkali metal oxide or alkalineearth metal oxide such as lithium oxide, calcium oxide, barium oxide,and the like can be given. A Lewis base such as magnesium oxide canalternatively be used. An organic compound such as tetrathiafulvalene(abbreviation: TTF) can alternatively be used.

Note that each of the above-described hole-injection layer 111,hole-transport layer 112, light-emitting layer 113, electron-transportlayer 114, electron-injection layer 115, and charge-generation layer (E)116 can be formed by a method such as an evaporation method (e.g., avacuum evaporation method), an ink-jet method, or a coating method.

In the above-described light-emitting element, current flows due to apotential difference generated between the first electrode 101 and thesecond electrode 103 and holes and electrons recombine in the EL layer102, whereby light is emitted. Then, the emitted light is extractedoutside through one or both of the first electrode 101 and the secondelectrode 103. Therefore, one or both of the first electrode 101 and thesecond electrode 103 are electrodes having a light-transmittingproperty.

The above-described light-emitting element can emit phosphorescenceoriginating from the organometallic complex and thus can have higherefficiency than a light-emitting element using a fluorescent compound.

Note that the light-emitting element described in this embodiment is anexample of a light-emitting element manufactured using theorganometallic complex that is one embodiment of the present invention.Further, as a light-emitting device including the above light-emittingelement, a passive matrix type light-emitting device and an activematrix type light-emitting device can be manufactured. It is alsopossible to manufacture a light-emitting device with a microcavitystructure including a light-emitting element which is a differentlight-emitting element from the above light-emitting elements asdescribed in another embodiment. Each of the above light-emittingdevices is included in the present invention.

Note that there is no particular limitation on the structure of the TFTin the case of manufacturing the active matrix light-emitting device.For example, a staggered TFT or an inverted staggered TFT can be used asappropriate. Further, a driver circuit formed over a TFT substrate maybe formed of both an n-type TFT and a p-type TFT or only either ann-type TFT or a p-type TFT. Furthermore, there is also no particularlimitation on crystallinity of a semiconductor film used for the TFT.For example, an amorphous semiconductor film, a crystallinesemiconductor film, an oxide semiconductor film, or the like can beused.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 3

In this embodiment, as one embodiment of the present invention, alight-emitting element in which two or more kinds of organic compoundsas well as a phosphorescent organometallic iridium complex are used fora light-emitting layer is described.

A light-emitting element described in this embodiment includes an ELlayer 203 between a pair of electrodes (an anode 201 and a cathode 202)as illustrated in FIG. 2. Note that the EL layer 203 includes at least alight-emitting layer 204 and may include a hole-injection layer, ahole-transport layer, an electron-transport layer, an electron-injectionlayer, a charge-generation layer (E), and the like. Note that for thehole-injection layer, the hole-transport layer, the electron-transportlayer, the electron-injection layer, and the charge-generation layer(E), the substances described in Embodiment 1 can be used.

The light-emitting layer 204 described in this embodiment contains aphosphorescent compound 205 using the phosphorescent organometalliciridium complex described in Embodiment 1, a first organic compound 206,and a second organic compound 207. Note that the phosphorescent compound205 is a guest material in the light-emitting layer 204. Moreover, oneof the first organic compound 206 and the second organic compound 207,the content of which is higher than that of the other in thelight-emitting layer 204, is a host material in the light-emitting layer204.

When the light-emitting layer 204 has the structure in which the guestmaterial is dispersed in the host material, crystallization of thelight-emitting layer can be suppressed. Further, it is possible tosuppress concentration quenching due to high concentration of the guestmaterial, and thus the light-emitting element can have higher emissionefficiency.

Note that it is preferable that a triplet excitation energy level (T₁level) of each of the first organic compound 206 and the second organiccompound 207 be higher than that of the phosphorescent compound 205.This is because, when the T₁ level of the first organic compound 206 (orthe second organic compound 207) is lower than that of thephosphorescent compound 205, the triplet excitation energy of thephosphorescent compound 205, which is to contribute to light emission,is quenched by the first organic compound 206 (or the second organiccompound 207) and accordingly the emission efficiency is decreased.

Here, for improvement in efficiency of energy transfer from a hostmaterial to a guest material, Förster mechanism (dipole-dipoleinteraction) and Dexter mechanism (electron exchange interaction), whichare known as mechanisms of energy transfer between molecules, areconsidered. According to the mechanisms, it is preferable that anemission spectrum of a host material (a fluorescence spectrum in energytransfer from a singlet excited state, and a phosphorescence spectrum inenergy transfer from a triplet excited state) largely overlap with anabsorption spectrum of a guest material (specifically, a spectrum in anabsorption band on the longest wavelength (lowest energy) side).However, in general, it is difficult to obtain an overlap between afluorescence spectrum of a host material and an absorption spectrum inan absorption band on the longest wavelength (lowest energy) side of aguest material. The reason for this is as follows: if the fluorescencespectrum of the host material overlaps with the absorption spectrum inthe absorption band on the longest wavelength (lowest energy) side ofthe guest material, since a phosphorescence spectrum of the hostmaterial is located on a longer wavelength (lower energy) side ascompared to the fluorescence spectrum, the T₁ level of the host materialbecomes lower than the T₁ level of the phosphorescent compound and theabove-described problem of quenching occurs; yet, when the host materialis designed in such a manner that the T₁ level of the host material ishigher than the T₁ level of the phosphorescent compound to avoid theproblem of quenching, the fluorescence spectrum of the host material isshifted to the shorter wavelength (higher energy) side, and thus thefluorescence spectrum does not have any overlap with the absorptionspectrum in the absorption band on the longest wavelength (lowestenergy) side of the guest material. For that reason, in general, it isdifficult to obtain an overlap between a fluorescence spectrum of a hostmaterial and an absorption spectrum in an absorption band on the longestwavelength (lowest energy) side of a guest material so as to maximizeenergy transfer from a singlet excited state of a host material.

Thus, in this embodiment, a combination of the first organic compoundand the second organic compound preferably forms an exciplex (alsoreferred to as excited complex). In that case, the first organiccompound 206 and the second organic compound 207 form an exciplex at thetime of recombination of carriers (electrons and holes) in thelight-emitting layer 204. Thus, in the light-emitting layer 204, afluorescence spectrum of the first organic compound 206 and that of thesecond organic compound 207 are converted into an emission spectrum ofthe exciplex which is located on a longer wavelength side. Moreover,when the first organic compound and the second organic compound areselected in such a manner that the emission spectrum of the exciplexlargely overlaps with the absorption spectrum of the guest material,energy transfer from a singlet excited state can be maximized. Note thatalso in the case of a triplet excited state, energy transfer from theexciplex, not the host material, is assumed to occur.

For the phosphorescent compound 205, the phosphorescent organometalliciridium complex described in Embodiment 1 is used. Although thecombination of the first organic compound 206 and the second organiccompound 207 can be determined such that an exciplex is formed, acombination of a compound which is likely to accept electrons (acompound having an electron-trapping property) and a compound which islikely to accept holes (a compound having a hole-trapping property) ispreferably employed.

As examples of a compound which is likely to accept electrons, thefollowing can be given:2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), and6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:6mDBTPDBq-II).

As examples of a compound which is likely to accept holes, the followingcan be given: 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBA1BP),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9′-bifluorene(abbreviation: DPA2SF),N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N-(9,9-dimethyl-2-N′,N″-diphenylamino-9H-fluoren-7-yl)diphenylamine(abbreviation: DPNF),N,N′,N″-triphenyl-N,N′,N″-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B),2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: PCASF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),N,N′-bis[4-(carbazol-9-yl)phenyl]-N,N′-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N′-phenyl-N′-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine(abbreviation: DFLADFL),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),4,4′bis(N-{4-[N′-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole(abbreviation: PCzTPN2), and3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2).

As for the above-described first and second organic compounds 206 and207, the present invention is not limited to the above examples. Thecombination is determined so that an exciplex can be formed, theemission spectrum of the exciplex overlaps with the absorption spectrumof the phosphorescent compound 205, and the peak of the emissionspectrum of the exciplex has a longer wavelength than the peak of theabsorption spectrum of the phosphorescent compound 205.

Note that in the case where a compound which is likely to acceptelectrons and a compound which is likely to accept holes are used forthe first organic compound 206 and the second organic compound 207,carrier balance can be controlled by the mixture ratio of the compounds.Specifically, the ratio of the first organic compound to the secondorganic compound is preferably 1:9 to 9:1.

In the light-emitting element described in this embodiment, energytransfer efficiency can be improved owing to energy transfer utilizingan overlap between an emission spectrum of an exciplex and an absorptionspectrum of a phosphorescent compound; accordingly, it is possible toachieve high external quantum efficiency of a light-emitting element.

Note that in another structure of the present invention, thelight-emitting layer 204 can be formed using a host molecule having ahole-trapping property and a host molecule having an electron-trappingproperty as the two kinds of organic compounds other than thephosphorescent compound 205 (guest material) so that a phenomenon (guestcoupled with complementary hosts: GCCH) occurs in which holes andelectrons are introduced to guest molecules existing in the two kinds ofhost molecules and the guest molecules are brought into an excitedstate.

At this time, the host molecule having a hole-trapping property and thehost molecule having an electron-trapping property can be respectivelyselected from the above-described compounds which are likely to acceptholes and the above-described compounds which are likely to acceptelectrons.

Note that the light-emitting element described in this embodiment is anexample of a structure of a light-emitting element; it is possible toapply a light-emitting element having another structure, which isdescribed in another embodiment, to a light-emitting device that is oneembodiment of the present invention. Further, as a light-emitting deviceincluding the above light-emitting element, a passive matrix typelight-emitting device and an active matrix type light-emitting devicecan be manufactured. It is also possible to manufacture a light-emittingdevice with a microcavity structure including the above light-emittingelement, whose structure is changed as described in another embodiment.Each of the above light-emitting devices is included in the presentinvention.

Note that there is no particular limitation on the structure of the TFTin the case of manufacturing the active matrix light-emitting device.For example, a staggered TFT or an inverted staggered TFT can be used asappropriate. Further, a driver circuit formed over a TFT substrate maybe formed of both an n-type TFT and a p-type TFT or only either ann-type TFT or a p-type TFT. Furthermore, there is also no particularlimitation on crystallinity of a semiconductor film used for the TFT.For example, an amorphous semiconductor film, a crystallinesemiconductor film, an oxide semiconductor film, or the like can beused.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 4

In this embodiment, as one embodiment of the present invention, alight-emitting element (hereinafter referred to as tandem light-emittingelement) in which a plurality of EL layers are included so as tosandwich a charge-generation layer will be described.

A light-emitting element described in this embodiment is a tandemlight-emitting element including a plurality of EL layers (a first ELlayer 302(1) and a second EL layer 302(2)) between a pair of electrodes(a first electrode 301 and a second electrode 304) as illustrated inFIG. 3A.

In this embodiment, the first electrode 301 functions as an anode, andthe second electrode 304 functions as a cathode. Note that the firstelectrode 301 and the second electrode 304 can have structures similarto those described in Embodiment 1. In addition, although the pluralityof EL layers (the first EL layer 302(1) and the second EL layer 302(2))may have structures similar to those described in Embodiment 1 or 2, anyof the EL layers may have a structure similar to that described inEmbodiment 1 or 2. In other words, the structures of the first EL layer302(1) and the second EL layer 302(2) may be the same or different fromeach other and can be similar to those described in Embodiment 1 or 2.

Further, a charge-generation layer (I) 305 is provided between theplurality of EL layers (the first EL layer 302(1) and the second ELlayer 302(2)). The charge-generation layer (I) 305 has a function ofinjecting electrons into one of the EL layers and injecting holes intothe other of the EL layers when a voltage is applied between the firstelectrode 301 and the second electrode 304. In this embodiment, when avoltage is applied such that the potential of the first electrode 301 ishigher than that of the second electrode 304, the charge-generationlayer (I) 305 injects electrons into the first EL layer 302(1) andinjects holes into the second EL layer 302(2).

Note that in terms of light extraction efficiency, the charge-generationlayer (I) 305 preferably has a light-transmitting property with respectto visible light (specifically, the charge-generation layer (I) 305 hasa visible light transmittance of 40% or more). Further, thecharge-generation layer (I) 305 functions even if it has lowerconductivity than the first electrode 301 or the second electrode 304.

The charge-generation layer (I) 305 may have either a structure in whichan electron acceptor (acceptor) is added to an organic compound having ahigh hole-transport property or a structure in which an electron donor(donor) is added to an organic compound having a high electron-transportproperty. Alternatively, both of these structures may be stacked.

In the case of the structure in which an electron acceptor is added toan organic compound having a high hole-transport property, as theorganic compound having a high hole-transport property, for example, anaromatic amine compound such as NPB, TPD, TDATA, MTDATA, or4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), or the like can be used. The substances mentionedhere are mainly ones that have a hole mobility of 10⁻⁶ cm²/Vs or higher.However, another substance may be used as long as the substance is anorganic compound having a higher hole-transport property than anelectron-transport property.

Further, as the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, or the like can be used. Alternatively, atransition metal oxide can be used. Further alternatively, an oxide ofmetals that belong to Group 4 to Group 8 of the periodic table can beused. Specifically, it is preferable to use vanadium oxide, niobiumoxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,manganese oxide, or rhenium oxide because the electron-acceptingproperty is high. Among these, molybdenum oxide is especially preferablebecause it is stable in the air, has a low hygroscopic property, and iseasily handled.

On the other hand, in the case of the structure in which an electrondonor is added to an organic compound having a high electron-transportproperty, as the organic compound having a high electron-transportproperty for example, a metal complex having a quinoline skeleton or abenzoquinoline skeleton, such as Alq, Almq₃, BeBq₂, or BAlq, or the likecan be used. Alternatively, it is possible to use a metal complex havingan oxazole-based ligand or a thiazole-based ligand, such as Zn(BOX)₂ orZn(BTZ)₂. Further alternatively, instead of a metal complex, it ispossible to use PBD, OXD-7, TAZ, Bphen, BCP, or the like. The substancesmentioned here are mainly ones that have an electron mobility of 10⁻⁶cm²/Vs or higher. Note that another substance may be used as long as thesubstance is an organic compound having a higher electron-transportproperty than a hole-transport property.

As the electron donor, it is possible to use an alkali metal, analkaline earth metal, a rare earth metal, a metal belonging to Group 2or 13 of the periodic table, or an oxide or carbonate thereof.Specifically, it is preferable to use lithium (Li), cesium (Cs),magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithiumoxide, cesium carbonate, or the like. Alternatively, an organic compoundsuch as tetrathianaphthacene may be used as the electron donor.

Note that forming the charge-generation layer (I) 305 by using any ofthe above materials can suppress an increase in drive voltage caused bythe stack of the EL layers.

Although this embodiment shows the light-emitting element having two ELlayers, the present invention can be similarly applied to alight-emitting element in which n EL layers (n is three or more) arestacked as illustrated in FIG. 3B. In the case where a plurality of ELlayers are included between a pair of electrodes as in thelight-emitting element according to this embodiment, by provision of acharge-generation layer (I) between the EL layers, light emission in ahigh luminance region can be obtained with current density kept low.Since the current density can be kept low, the element can have a longlifetime. When the light-emitting element is applied for lighting,voltage drop due to resistance of an electrode material can be reduced,thereby achieving homogeneous light emission in a large area. Moreover,it is possible to achieve a light-emitting device of low powerconsumption, which can be driven at a low voltage.

By making the EL layers emit light of different colors from each other,the light-emitting element can provide light emission of a desired coloras a whole. For example, by forming a light-emitting element having twoEL layers such that the emission color of the first EL layer and theemission color of the second EL layer are complementary colors, thelight-emitting element can provide white light emission as a whole. Notethat the word “complementary” means color relationship in which anachromatic color is obtained when colors are mixed. In other words, whenlights obtained from substances which emit light of complementary colorsare mixed, white emission can be obtained.

Further, the same can be applied to a light-emitting element havingthree EL layers. For example, the light-emitting element as a whole canprovide white light emission when the emission color of the first ELlayer is red, the emission color of the second EL layer is green, andthe emission color of the third EL layer is blue.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 5

In this embodiment, as a light-emitting device utilizing phosphorescencewhich is one embodiment of the present invention, a light-emittingdevice using a phosphorescent organometallic iridium complex isdescribed.

A light-emitting device described in this embodiment has a micro opticalresonator (microcavity) structure in which a light resonant effectbetween a pair of electrodes is utilized. The light-emitting deviceincludes a plurality of light-emitting elements each of which has atleast an EL layer 405 between a pair of electrodes (a reflectiveelectrode 401 and a semi-transmissive and semi-reflective electrode 402)as illustrated in FIG. 4. Further, the EL layer 405 includes at least alight-emitting layer 404 serving as a light-emitting region and mayfurther include a hole-injection layer, a hole-transport layer, anelectron-transport layer, an electron-injection layer, acharge-generation layer (E), and the like. Note that the light-emittinglayer 404 contains a phosphorescent organometallic iridium complex thatis one embodiment of the present invention.

In this embodiment, a light-emitting device is described which includeslight-emitting elements (a first light-emitting element (R) 410R, asecond light-emitting element (G) 410G, and a third light-emittingelement (B) 410B) having different structures as illustrated in FIG. 4.

The first light-emitting element (R) 410R has a structure in which afirst transparent conductive layer 403 a; an EL layer 405 including afirst light-emitting layer (B) 404B, a second light-emitting layer (G)404G, and a third light-emitting layer (R) 404R; and a semi-transmissiveand semi-reflective electrode 402 are sequentially stacked over areflective electrode 401. The second light-emitting element (G) 410G hasa structure in which a second transparent conductive layer 403 b, the ELlayer 405, and the semi-transmissive and semi-reflective electrode 402are sequentially stacked over the reflective electrode 401. The thirdlight-emitting element (B) 410B has a structure in which the EL layer405 and the semi-transmissive and semi-reflective electrode 402 aresequentially stacked over the reflective electrode 401.

Note that the reflective electrode 401, the EL layer 405, and thesemi-transmissive and semi-reflective electrode 402 are common to thelight-emitting elements (the first light-emitting element (R) 410R, thesecond light-emitting element (G) 410G, and the third light-emittingelement (B) 410B). The first light-emitting layer (B) 404B emits light(λ_(B)) having a peak in a wavelength range from 420 nm to 480 nm. Thesecond light-emitting layer (G) 404G emits light (λ_(G)) having a peakin a wavelength range from 500 nm to 550 nm. The third light-emittinglayer (R) 404R emits light (λ_(R)) having a peak in a wavelength rangefrom 600 nm to 760 nm. Thus, in each of the light-emitting elements (thefirst light-emitting element (R) 410R, the second light-emitting element(G) 410G, and the third light-emitting element (B) 410B), light emittedfrom the first light-emitting layer (B) 404B, light emitted from thesecond light-emitting layer (G) 404G, and light emitted from the thirdlight-emitting layer (R) 404R overlap with each other; accordingly,light having a broad emission spectrum that covers a visible light rangecan be emitted. Note that the above wavelengths satisfy the relation ofλ_(B)<λ_(G)<λ_(R).

Each of the light-emitting elements described in this embodiment has astructure in which the EL layer 405 is interposed between the reflectiveelectrode 401 and the semi-transmissive and semi-reflective electrode402. Light emitted in all directions from the light-emitting layersincluded in the EL layer 405 is resonated by the reflective electrode401 and the semi-transmissive and semi-reflective electrode 402 whichfunction as a micro optical resonator (microcavity). Note that thereflective electrode 401 is formed using a conductive material havingreflectivity, and a film whose visible light reflectivity is 40% to100%, preferably 70% to 100%, and whose resistivity is 1×10⁻² Ωcm orlower is used. In addition, the semi-transmissive and semi-reflectiveelectrode 402 is formed using a conductive material having reflectivityand a conductive material having a light-transmitting property, and afilm whose visible light reflectivity is 20% to 80%, preferably 40% to70%, and whose resistivity is 1×10⁻² Ωcm or lower is used.

In this embodiment, the thicknesses of the transparent conductive layers(the first transparent conductive layer 403 a and the second transparentconductive layer 403 b) provided in the first light-emitting element (R)410R and the second light-emitting element (G) 410G, respectively, arevaried between the light-emitting elements, whereby the light-emittingelements differ in the optical path length from the reflective electrode401 to the semi-transmissive and semi-reflective electrode 402. In otherwords, in light having a broad emission spectrum, which is emitted fromthe light-emitting layers of each of the light-emitting elements, lightwith a wavelength that is resonated between the reflective electrode 401and the semi-transmissive and semi-reflective electrode 402 can beenhanced while light with a wavelength that is not resonatedtherebetween can be attenuated. Thus, when the elements differ in theoptical path length from the reflective electrode 401 to thesemi-transmissive and semi-reflective electrode 402, light withdifferent wavelengths can be extracted.

Note that the total thickness from the reflective electrode 401 to thesemi-transmissive and semi-reflective electrode 402 is set to mλ_(R)/2(m is a natural number) in the first light-emitting element (R) 410R;the total thickness from the reflective electrode 401 to thesemi-transmissive and semi-reflective electrode 402 is set to mλ_(G)/2(m is a natural number) in the second light-emitting element (G) 410G;and the total thickness from the reflective electrode 401 to thesemi-transmissive and semi-reflective electrode 402 is set to mλ_(B)/2(m is a natural number) in the third light-emitting element (B) 410B.

In this manner, the light (λ_(R)) emitted from the third light-emittinglayer (R) 404R included in the EL layer 405 is mainly extracted from thefirst light-emitting element (R) 410R, the light (λ_(G)) emitted fromthe second light-emitting layer (G) 404G included in the EL layer 405 ismainly extracted from the second light-emitting element (G) 410G, andthe light (λ_(B)) emitted from the first light-emitting layer (B) 404Bincluded in the EL layer 405 is mainly extracted from the thirdlight-emitting element (B) 410B. Note that the light extracted from eachof the light-emitting elements is emitted from the semi-transmissive andsemi-reflective electrode 402 side.

Further, strictly speaking, the total thickness from the reflectiveelectrode 401 to the semi-transmissive and semi-reflective electrode 402can be the total thickness from a reflection region in the reflectiveelectrode 401 to a reflection region in the semi-transmissive andsemi-reflective electrode 402. However, it is difficult to preciselydetermine the positions of the reflection regions in the reflectiveelectrode 401 and the semi-transmissive and semi-reflective electrode402; therefore, it is assumed that the above effect can be sufficientlyobtained wherever the reflection regions may be set in the reflectiveelectrode 401 and the semi-transmissive and semi-reflective electrode402.

Next, in the first light-emitting element (R) 410R, the optical pathlength from the reflective electrode 401 to the third light-emittinglayer (R) 404R is adjusted to a desired thickness ((2m′+1)λ_(R)/4, wherem′ is a natural number); thus, light emitted from the thirdlight-emitting layer (R) 404R can be amplified. Light (first reflectedlight) that is reflected by the reflective electrode 401 of the lightemitted from the third light-emitting layer (R) 404R interferes withlight (first incident light) that directly enters the semi-transmissiveand semi-reflective electrode 402 from the third light-emitting layer(R) 404R. Therefore, by adjusting the optical path length from thereflective electrode 401 to the third light-emitting layer (R) 404R tothe desired value ((2m′+1)λ_(R)/4, where m′ is a natural number), thephases of the first reflected light and the first incident light can bealigned with each other and the light emitted from the thirdlight-emitting layer (R) 404R can be amplified.

Note that, strictly speaking, the optical path length from thereflective electrode 401 to the third light-emitting layer (R) 404R canbe the optical path length from a reflection region in the reflectiveelectrode 401 to a light-emitting region in the third light-emittinglayer (R) 404R. However, it is difficult to precisely determine thepositions of the reflection region in the reflective electrode 401 andthe light-emitting region in the third light-emitting layer (R) 404R;therefore, it is assumed that the above effect can be sufficientlyobtained wherever the reflection region and the light-emitting regionmay be set in the reflective electrode 401 and the third light-emittinglayer (R) 404R, respectively.

Next, in the second light-emitting element (G) 410G, the optical pathlength from the reflective electrode 401 to the second light-emittinglayer (G) 404G is adjusted to a desired thickness. ((2m″+1)λ_(G)/4,where m″ is a natural number); thus, light emitted from the secondlight-emitting layer (G) 404G can be amplified. Light (second reflectedlight) that is reflected by the reflective electrode 401 of the lightemitted from the second light-emitting layer (G) 404G interferes withlight (second incident light) that directly enters the semi-transmissiveand semi-reflective electrode 402 from the second light-emitting layer(G) 404G. Therefore, by adjusting the optical path length from thereflective electrode 401 to the second light-emitting layer (G) 404G tothe desired value ((2m″+1)λ_(G)/4, where m″ is a natural number), thephases of the second reflected light and the second incident light canbe aligned with each other and the light emitted from the secondlight-emitting layer (G) 404G can be amplified.

Note that, strictly speaking, the optical path length from thereflective electrode 401 to the second light-emitting layer (G) 404G canbe the optical path length from a reflection region in the reflectiveelectrode 401 to a light-emitting region in the second light-emittinglayer (G) 404G However, it is difficult to precisely determine thepositions of the reflection region in the reflective electrode 401 andthe light-emitting region in the second light-emitting layer (G) 404G;therefore, it is assumed that the above effect can be sufficientlyobtained wherever the reflection region and the light-emitting regionmay be set in the reflective electrode 401 and the second light-emittinglayer (G) 404G respectively.

Next, in the third light-emitting element (B) 410B, the optical pathlength from the reflective electrode 401 to the first light-emittinglayer (B) 404B is adjusted to a desired thickness ((2m′″+1)λ_(B)/4,where m′″ is a natural number); thus, light emitted from the firstlight-emitting layer (B) 404B can be amplified. Light (third reflectedlight) that is reflected by the reflective electrode 401 of the lightemitted from the first light-emitting layer (B) 404B interferes withlight (third incident light) that directly enters the semi-transmissiveand semi-reflective electrode 402 from the first light-emitting layer(B) 404B. Therefore, by adjusting the optical path length from thereflective electrode 401 to the first light-emitting layer (B) 404B tothe desired value ((2m′″+1)λ_(B)/4, where m′″ is a natural number), thephases of the third reflected light and the third incident light can bealigned with each other and the light emitted from the firstlight-emitting layer (B) 404B can be amplified.

Note that, strictly speaking, the optical path length from thereflective electrode 401 to the first light-emitting layer (B) 404B inthe third light-emitting element can be the optical path length from areflection region in the reflective electrode 401 to a light-emittingregion in the first light-emitting layer (B) 404B. However, it isdifficult to precisely determine the positions of the reflection regionin the reflective electrode 401 and the light-emitting region in thefirst light-emitting layer (B) 404B; therefore, it is assumed that theabove effect can be sufficiently obtained wherever the reflection regionand the light-emitting region may be set in the reflective electrode 401and the first light-emitting layer (B) 404B, respectively.

Note that although each of the light-emitting elements in theabove-described structure includes a plurality of light-emitting layersin the EL layer, the present invention is not limited thereto; forexample, the structure of the tandem light-emitting element which isdescribed in Embodiment 4 can be combined, in which case a plurality ofEL layers are provided so as to sandwich a charge-generation layer inone light-emitting element and one or more light-emitting layers areformed in each of the EL layers.

The light-emitting device described in this embodiment has a microcavitystructure, in which light with wavelengths which differ depending on thelight-emitting elements can be extracted even when they include the sameEL layers, so that it is not needed to form light-emitting elements forthe colors of R, and B. Therefore, the above structure is advantageousfor full color display owing to easiness in achieving higher resolutiondisplay or the like. In addition, emission intensity with apredetermined wavelength in the front direction can be increased,whereby power consumption can be reduced. The above structure isparticularly useful in the case of being applied to a color display(image display device) including pixels of three or more colors but mayalso be applied to lighting or the like.

Embodiment 6

In this embodiment, a light-emitting device including a light-emittingelement in which an organometallic complex that is one embodiment of thepresent invention is used for a light-emitting layer is described.

The light-emitting device can be either a passive matrix light-emittingdevice or an active matrix light-emitting device. Note that any of thelight-emitting elements described in the other embodiments can beapplied to the light-emitting device described in this embodiment.

In this embodiment, an active matrix light-emitting device is describedwith reference to FIGS. 5A and 5B.

Note that FIG. 5A is a top view illustrating a light-emitting device andFIG. 5B is a cross-sectional view taken along the chain line A-A′ inFIG. 5A. The active matrix light-emitting device according to thisembodiment includes a pixel portion 502 provided over an elementsubstrate 501, a driver circuit portion (a source line driver circuit)503, and a driver circuit portion (a gate line driver circuit) 504. Thepixel portion 502, the driver circuit portion 503, and the drivercircuit portion 504 are sealed between the element substrate 501 and thesealing substrate 506 by a sealant 505.

In addition, there is provided a lead wiring 507 over the elementsubstrate 501. The lead wiring 507 is provided for connecting anexternal input terminal through which a signal (e.g., a video signal, aclock signal, a start signal, and a reset signal) or a potential fromthe outside is transmitted to the driver circuit portion 503 and thedriver circuit portion 504. Here is shown an example in which a flexibleprinted circuit (FPC) 508 is provided as the external input terminal.Although the FPC 508 is illustrated alone, this FPC may be provided witha printed wiring board (PWB). The light-emitting device in the presentspecification includes, in its category, not only the light-emittingdevice itself but also the light-emitting device provided with the FPCor the PWB.

Next, a cross-sectional structure is described with reference to FIG.5B. The driver circuit portion and the pixel portion are formed over theelement substrate 501; here are illustrated the driver circuit portion503 which is the source line driver circuit and the pixel portion 502.

The driver circuit portion 503 is an example where a CMOS circuit isformed, which is a combination of an n-channel TFT 509 and a p-channelTFT 510. Note that the driver circuit portion may be formed usingvarious circuits including TFTs, such as a CMOS circuit, a PMOS circuit,or an NMOS circuit. Although this embodiment shows a driver integratedtype in which the driver circuit is formed over the substrate, thedriver circuit is not necessarily formed over the substrate, and thedriver circuit can be formed outside, not over the substrate.

The pixel portion 502 is formed of a plurality of pixels each of whichincludes a switching TFT 511, a current control TFT 512, and a firstelectrode (anode) 513 which is electrically connected to a wiring (asource electrode or a drain electrode) of the current control TFT 512.Note that an insulator 514 is formed to cover end portions of the firstelectrode (anode) 513. In this embodiment, the insulator 514 is formedusing a positive photosensitive acrylic resin.

The insulator 514 preferably has a curved surface with curvature at anupper end portion or a lower end portion thereof in order to obtainfavorable coverage by a film which is to be stacked over the insulator514. For example, in the case of using a positive photosensitive acrylicresin as a material for the insulator 514, the insulator 514 preferablyhas a curved surface with a curvature radius (0.2 μm to 3 μm) at theupper end portion. Note that the insulator 514 can be formed usingeither a negative photosensitive material that becomes insoluble in anetchant by light irradiation or a positive photosensitive material thatbecomes soluble in an etchant by light irradiation. It is possible touse, without limitation to an organic compound, either an organiccompound or an inorganic compound such as silicon oxide or siliconoxynitride.

An EL layer 515 and a second electrode (cathode) 516 are stacked overthe first electrode (anode) 513. In the EL layer 515, at least alight-emitting layer is provided which contains an organometalliccomplex that is one embodiment of the present invention. Further, in theEL layer 515, a hole-injection layer, a hole-transport layer, anelectron-transport layer, an electron-injection layer, acharge-generation layer, and the like can be provided as appropriate inaddition to the light-emitting layer.

A light-emitting element 517 is formed of a stacked structure of thefirst electrode (anode) 513, the EL layer 515, and the second electrode(cathode) 516. For the first electrode (anode) 513, the EL layer 515,and the second electrode (cathode) 516, the materials described inEmbodiment 1 can be used. Although not illustrated, the second electrode(cathode) 516 is electrically connected to an FPC 508 which is anexternal input terminal.

Although the cross-sectional view of FIG. 5B illustrates only onelight-emitting element 517, a plurality of light-emitting elements arearranged in matrix in the pixel portion 502. Light-emitting elementswhich provide three kinds of light emission (R, G, and B) areselectively formed in the pixel portion 502, whereby a light-emittingdevice capable of full color display can be fabricated. Alternatively, alight-emitting device which is capable of full color display may befabricated by a combination with color filters.

Further, the sealing substrate 506 is attached to the element substrate501 with the sealant 505, whereby a light-emitting element 517 isprovided in a space 518 surrounded by the element substrate 501, thesealing substrate 506, and the sealant 505. The space 518 may be filledwith an inert gas (such as nitrogen or argon), or the sealant 505.

An epoxy-based resin is preferably used for the sealant 505. It ispreferable that such a material do not transmit moisture or oxygen asmuch as possible. As the sealing substrate 506, a glass substrate, aquartz substrate, or a plastic substrate formed of fiberglass reinforcedplastic (FRP), polyvinyl fluoride (PVF), polyester, acrylic, or the likecan be used.

As described above, an active matrix light-emitting device can beobtained.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 7

In this embodiment, examples of a variety of electronic devices whichare completed using a light-emitting device will be described withreference to FIGS. 6A to 6D. To the light-emitting device, anorganometallic complex that is one embodiment of the present inventionis applied.

Examples of the electronic devices to which the light-emitting device isapplied are a television device (also referred to as television ortelevision receiver), a monitor of a computer or the like, a camera suchas a digital camera or a digital video camera, a digital photo frame, amobile phone (also referred to as cellular phone or cellular phonedevice), a portable game machine, a portable information terminal, anaudio reproducing device, and a large-sized game machine such as apachinko machine. Specific examples of these electronic devices areillustrated in FIGS. 6A to 6D.

FIG. 6A illustrates an example of a television set. In a television set7100, a display portion 7103 is incorporated in a housing 7101. Imagescan be displayed on the display portion 7103, and the light-emittingdevice can be used for the display portion 7103. In addition, here, thehousing 7101 is supported by a stand 7105.

Operation of the television set 7100 can be performed with an operationswitch of the housing 7101 or a separate remote controller 7110. Withoperation keys 7109 of the remote controller 7110, channels and volumecan be controlled and images displayed on the display portion 7103 canbe controlled. Furthermore, the remote controller 7110 may be providedwith a display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television set 7100 is provided with a receiver, a modem,and the like. With the receiver, a general television broadcast can bereceived. Furthermore, when the television set 7100 is connected to acommunication network by wired or wireless connection via the modem,one-way (from a transmitter to a receiver) or two-way (between atransmitter and a receiver, between receivers, or the like) datacommunication can be performed.

FIG. 6B illustrates a computer having a main body 7201, a housing 7202,a display portion 7203, a keyboard 7204, an external connection port7205, a pointing device 7206, and the like. Note that this computer ismanufactured using the light-emitting device for the display portion7203.

FIG. 6C illustrates a portable game machine having two housings, ahousing 7301 and a housing 7302, which are connected with a jointportion 7303 so that the portable game machine can be opened or folded.A display portion 7304 is incorporated in the housing 7301, and adisplay portion 7305 is incorporated in the housing 7302. In addition,the portable game machine illustrated in FIG. 6C includes a speakerportion 7306, a recording medium insertion portion 7307, an LED lamp7308, input means (an operation key 7309, a connection terminal 7310, asensor 7311 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), and a microphone 7312), and thelike. Needless to say, the structure of the portable game machine is notlimited to the above as long as the light-emitting device is used for atleast one of the display portion 7304 and the display portion 7305, andmay include other accessories as appropriate. The portable game machineillustrated in FIG. 6C has a function of reading out a program or datastored in a storage medium to display it on the display portion, and afunction of sharing information with another portable game machine bywireless communication. The portable game machine illustrated in FIG. 6Ccan have a variety of functions without limitation to the above.

FIG. 6D illustrates an example of a mobile phone. A mobile phone 7400 isprovided with a display portion 7402 incorporated in a housing 7401,operation buttons 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. Note that the mobile phone 7400is manufactured using the light-emitting device for the display portion7402.

When the display portion 7402 of the mobile phone 7400 illustrated inFIG. 6D is touched with a finger or the like, data can be input to themobile phone 7400. Further, operations such as making a call andcomposing an e-mail can be performed by touching the display portion7402 with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying images. The secondmode is an input mode mainly for inputting data such as text. The thirdmode is a display-and-input mode in which two modes of the display modeand the input mode are combined.

For example, in the case of making a call or composing an e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on the screen can be input. In this case, itis preferable to display a keyboard or number buttons on almost theentire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside themobile phone 7400, display on the screen of the display portion 7402 canbe automatically switched by determining the orientation of the mobilephone 7400 (whether the mobile phone is placed horizontally orvertically for a landscape mode or a portrait mode).

The screen modes are switched by touching the display portion 7402 oroperating the operation buttons 7403 of the housing 7401. The screenmodes can also be switched depending on the kind of image displayed onthe display portion 7402. For example, when a signal of an imagedisplayed on the display portion is a signal of moving image data, thescreen mode is switched to the display mode. When the signal is a signalof text data, the screen mode is switched to the input mode.

Moreover, in the input mode, when input by touching the display portion7402 is not performed for a certain period while a signal detected by anoptical sensor in the display portion 7402 is detected, the screen modemay be controlled so as to be switched from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken when thedisplay portion 7402 is touched with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source which emits near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

As described above, the electronic devices can be obtained byapplication of the light-emitting device according to one embodiment ofthe present invention. The light-emitting device has a remarkably wideapplication range, and can be applied to electronic devices in a varietyof fields.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 8

In this embodiment, examples of a lighting device to which alight-emitting device including an organometallic complex that is oneembodiment of the present invention is applied will be described withreference to FIG. 7.

FIG. 7 illustrates an example in which the light-emitting device is usedas an indoor lighting device 8001. Since the light-emitting device canhave a larger area, it can be used for a lighting device having a largearea. In addition, a lighting device 8002 in which a light-emittingregion has a curved surface can also be obtained with the use of ahousing with a curved surface. A light-emitting element included in thelight-emitting device described in this embodiment is in a thin filmform, which allows the housing to be designed more freely. Therefore,the lighting device can be elaborately designed in a variety of ways.Further, a wall of the room may be provided with a large-sized lightingdevice 8003.

Moreover, when the light-emitting device is used for a table by beingused as a surface of a table, a lighting device 8004 which has afunction as a table can be obtained. When the light-emitting device isused as part of other furniture, a lighting device which has a functionas the furniture can be obtained.

In this manner, a variety of lighting devices to which thelight-emitting device is applied can be obtained. Note that suchlighting devices are also embodiments of the present invention.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Example 1 Synthesis Example 1

In this example, a synthesis method is described of the organometalliccomplex represented by Structural Formula (100) in Embodiment 1 which isone embodiment of the present invention,(acetylacetonato)bis(2,4-diphenyl-1,3,5-triazinato)iridium(III)(abbreviation: [Ir(dptzn)₂(acac)]). The structure of [Ir(dptzn)₂(acac)](abbreviation) is shown below.

Step 1: Synthesis of 2,4-Diphenyl-1,3,5-triazine (Abbreviation: Hdptzn)

First, 9.63 g of benzamidine hydrochloride and 10.19 g of Gold's Reagent(another name: (dimethylaminomethyleneaminomethylene)dimethylammoniumchloride, produced by Sigma-Aldrich Inc.) were put in a flask and theair in the flask was replaced with nitrogen. This reaction container washeated at 120° C. for 3 hours to cause a reaction. Water was added tothe reacted solution and filtration was performed. The obtained residuewas washed with methanol to give an objective triazine derivative Hdptzn(abbreviation) (white powder, 30% in yield). The synthesis scheme ofStep 1 is shown by (a-1) below.

Step 2: Synthesis ofDi-μ-chloro-bis[bis(2,4-diphenyl-1,3,5-triazinato)iridium(III)](Abbreviation: [Ir(dptzn)₂Cl]₂)

Next, in a flask equipped with a reflux pipe were put 15 mL of2-ethoxyethanol, 5 mL of water, 2.51 g of Hdptzn obtained in Step 1above, and 1.18 g of iridium chloride hydrate (IrCl₃.H₂O), and the airin the flask was replaced with argon. Then, irradiation with microwaves(2.45 GHz, 100 W) for 30 minutes was performed to cause a reaction. Thereacted solution was filtered and the obtained residue was washed withethanol to give a dinuclear complex [Ir(dptzn)₂Cl]₂ (abbreviation)(brown powder, 44% in yield). The synthesis scheme of Step 2 is shown by(b-1) below.

Step 3: Synthesis of(Acetylacetonato)bis(2,4-diphenyl-1,3,5-triazinato)iridium(III)(Abbreviation: [Ir(dptzn)₂(acac)]))

Further, 20 mL of 2-ethoxyethanol, 1.21 g of the dinuclear complex[Ir(dptzn)₂Cl]₂ (abbreviation) obtained in Step 2 above, 0.27 mL ofacetylacetone, and 0.92 g of sodium carbonate were put in a recoveryflask equipped with a reflux pipe, and the air in the flask was replacedwith argon. Then, irradiation with microwaves (2.45 GHz, 100 W) for 30minutes was performed to cause a reaction. Dichloromethane was added tothe reacted solution and filtration was performed. The solvent of thefiltrate was distilled off, and then the obtained residue was purifiedby flash column chromatography (silica gel) using a mixed solvent ofhexane and dichloromethane as a developing solvent in a volume ratio of1:25, to give the organometallic complex [Ir(dptzn)₂(acac)](abbreviation), which is one embodiment of the present invention, asorange powder (10% in yield). The synthesis scheme of Step 3 is shown by(c-1) below.

An analysis result by nuclear magnetic resonance (¹H NMR) spectroscopyof the orange powder obtained in Step 3 above is described below. FIG. 8shows the ¹H NMR chart. These results revealed that the organometalliccomplex represented by Structural Formula (100) above which is oneembodiment of the present invention, [Ir(dptzn)₂(acac)] (abbreviation),was obtained in Synthesis Example 1.

¹H NMR. δ(CDCl₃): 1.85 (s, 6H), 5.31 (s, 1H), 6.56 (dd, 2H), 6.88-6.99(m, 4H), 7.58-7.68 (m, 6H), 8.23 (dd, 2H), 8.72 (dd, 4H), 9.13 (s, 2H).

Next, an ultraviolet-visible absorption spectrum (hereinafter, simplyreferred to as an “absorption spectrum”) of a dichloromethane solutionof [Ir(dptzn)₂(acac)] (abbreviation) and an emission spectrum thereofwere measured. The measurement of the absorption spectrum was conductedat room temperature, for which an ultraviolet-visible lightspectrophotometer (V550 type manufactured by Japan SpectroscopyCorporation) was used and the dichloromethane solution (0.120 mmol/L)was put in a quartz cell. In addition, the measurement of the emissionspectrum was conducted at room temperature, for which a fluorescencespectrophotometer (FS920 manufactured by Hamamatsu PhotonicsCorporation) was used and the degassed dichloromethane solution (0.120mmol/L) was put in a quartz cell.

Measurement results of the obtained absorption and emission spectra areshown in FIG. 9, in which the horizontal axis represents wavelength andthe vertical axes represent absorption intensity and emission intensity.In FIG. 9 where there are two solid lines, the thin line represents theabsorption spectrum and the thick line represents the emission spectrum.Note that the absorption spectrum in FIG. 9 is the results obtained insuch a way that the absorption spectrum measured by putting onlydichloromethane in a quartz cell was subtracted from the absorptionspectrum measured by putting the dichloromethane solution (0.120 mmol/L)in a quartz cell.

As shown in FIG. 9, the organometallic complex of one embodiment of thepresent invention, [Ir(dptzn)₂(acac)] (abbreviation), has an emissionpeak at 605 nm, and orange light emission was observed from thedichloromethane solution.

Example 2

In this example, a light-emitting element in which the phosphorescentorganometallic iridium complex [Ir(dptzn)₂(acac)] (Structural Formula(100)) is used for a light-emitting layer is described with reference toFIG. 10. Chemical formulae of materials used in this example are shownbelow.

<<Manufacture of Light-Emitting Element>>

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 1100 by a sputtering method, so that a firstelectrode 1101 which functions as an anode was formed. The thickness was110 nm and the electrode area was 2 mm×2 mm.

Then, as pretreatment for forming the light-emitting element over thesubstrate 1100, UV ozone treatment was performed for 370 seconds afterwashing of a surface of the substrate with water and baking that wasperformed at 200° C. for one hour.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 30 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate 1100 was cooled down for about 30 minutes.

Next, the substrate 1100 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 1100 over whichthe first electrode 1101 was formed faced downward. In this example, acase will be described in which a hole-injection layer 1111, ahole-transport layer 1112, a light-emitting layer 1113, anelectron-transport layer 1114, and an electron-injection layer 1115which are included in an EL layer 1102 are sequentially formed by avacuum evaporation method.

After reducing the pressure of the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum(VI) oxide were co-evaporated with a mass ratio of DBT3P-II(abbreviation) to molybdenum oxide being 4:2, whereby the hole-injectionlayer 1111 was formed over the first electrode 1101. The thickness ofthe hole-injection layer 1111 was 40 nm. Note that the co-evaporation isan evaporation method in which some different substances are evaporatedfrom some different evaporation sources at the same time.

Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) was evaporated to a thickness of 20 nm, so that thehole-transport layer 1112 was formed.

Next, the light-emitting layer 1113 was formed over the hole-transportlayer 1112. Co-evaporated were2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-H), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl(abbreviation: NPB), and(acetylacetonato)bis(2,4-diphenyl-1,3,5-triazinato)iridium(III)(abbreviation: [Ir(dptzn)₂(acac)]) with a mass ratio of 2mDBTPDBq-II(abbreviation) to NPB (abbreviation) and [Ir(dptzn)₂(acac)](abbreviation) being 0.8:0.2:0.01, whereby the light-emitting layer 1113was formed. The thickness of the light-emitting layer 1113 was 40 nm.

Then, 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-II) was evaporated to a thickness of 10 nm overthe light-emitting layer 1113 and bathophenanthroline (abbreviation:Bphen) was evaporated to a thickness of 20 nm, whereby theelectron-transport layer 1114 was formed. Furthermore, lithium fluoridewas evaporated to a thickness of 1 nm over the electron-transport layer1114, whereby the electron-injection layer 1115 was formed.

Finally, aluminum was evaporated to a thickness of 200 nm over theelectron-injection layer 1115 to form the second electrode 1103 servinga cathode; thus, the light-emitting element was obtained. Note that inall the above evaporation steps, evaporation was performed by aresistance-heating method.

An element structure of the light-emitting element obtained as describedabove is shown in Table 1.

TABLE 1 Hole- Electron- First injection Hole-transport injection SecondElectrode Layer Layer Light-emitting Layer Electron-transport LayerLayer Electrode Light- ITSO DBT3P-II:MoOx BPAFLP2mDBTPDBq-II:NPB:[Ir(dptzn)₂(acac)] 2mDBTPDBq-II Bphen LiF Al emitting(110 nm) (4:2 40 nm) (20 nm) (0.8:0.2:0.01 40 nm) (10 nm) (20 nm) (1 nm)(200 nm) Element

Further, the manufactured light-emitting element was sealed in a glovebox containing a nitrogen atmosphere so as not to be exposed to the air.

<<Operation Characteristics of Light-Emitting Element>>

Operation characteristics of the manufactured light-emitting elementwere measured. Note that the measurement was carried out at roomtemperature (under an atmosphere in which the temperature was kept at25° C.).

FIG. 11 shows luminance vs. current efficiency characteristics of thelight-emitting element. In FIG. 11, the vertical axis represents currentefficiency (cd/A) and the horizontal axis represents luminance (cd/m²).FIG. 12 shows voltage vs. luminance characteristics of thelight-emitting element. In FIG. 12, the vertical axis representsluminance (cd/m²) and the horizontal axis represents voltage (V). Table2 below shows initial values of main characteristics of thelight-emitting element at a luminance of about 1000 cd/m².

TABLE 2 Cur- External rent Quan- Den- tum Volt- Cur- sity Chroma- Lumi-Power Effi- age rent (mA/ ticity nance Efficienty ciency (V) (mA) cm²)(x, y) (cd/m²) (lm/W) (%) Light- 3.3 0.07 1.7 (0.55, 940 52.9 22emitting 0.44) Element

From the above results, the light-emitting element manufactured in thisexample has high external quantum efficiency, which means its highemission efficiency. Moreover, as for color purity, it can be found thatthe light-emitting element exhibits orange emission with excellent colorpurity.

FIG. 13 shows an emission spectrum when a current at a current densityof 25 mA/cm² was supplied to the light-emitting element. As shown inFIG. 13, the emission spectrum of the light-emitting element has a peakat 583 nm and it is indicated that the emission spectrum is derived fromemission of the phosphorescent organometallic iridium complex[Ir(dptzn)₂(acac)] (abbreviation).

REFERENCE NUMERALS

-   -   101: first electrode, 102: EL layer, 103: second electrode, 111:        hole-injection layer, 112: hole-transport layer, 113:        light-emitting layer, 114: electron-transport layer, 115:        electron-injection layer, 116: charge-generation layer, 201:        anode, 202: cathode, 203: EL layer, 204: light-emitting layer,        205: phosphorescent compound, 206: first organic compound, 207:        second organic compound, 301: first electrode, 302(1): first EL        layer, 302(2): second EL layer, 304: second electrode, 305:        charge-generation layer (I), 401: reflective electrode, 402:        semi-transmissive and semi-reflective electrode, 403 a: first        transparent conductive layer, 403 b: second transparent        conductive layer, 404B: first light-emitting layer (B), 404G:        second light-emitting layer (G), 404R: third light-emitting        layer (R), 405: EL layer, 410R: first light-emitting element        (R), 410G: second light-emitting element (G), 410B: third        light-emitting element (B), 501: element substrate, 502: pixel        portion, 503: driver circuit portion (source line driver        circuit), 504: driver circuit portion (gate line driver        circuit), 505: sealant, 506: sealing substrate, 507: wiring,        508: FPC (flexible printed circuit), 509: n-channel TFT, 510:        p-channel TFT, 511: switching TFT, 512: current control TFT,        513: first electrode (anode), 514: insulator, 515: EL layer,        516: second electrode (cathode), 517: light-emitting element,        518: space, 1100: substrate, 1101: first electrode, 1102: EL        layer, 1103: second electrode, 1111: hole-injection layer, 1112:        hole-transport layer, 1113: light-emitting layer, 1114:        electron-transport layer, 1115: electron-injection layer, 7100:        television device, 7101: housing, 7103: display portion, 7105:        stand, 7107: display portion, 7109: operation key, 7110: remote        controller, 7201: main body, 7202: housing, 7203: display        portion, 7204: keyboard, 7205: external connection port, 7206:        pointing device, 7301: housing, 7302: housing, 7303: joint        portion, 7304: display portion, 7305: display portion, 7306:        speaker portion, 7307: recording medium insertion portion, 7308:        LED lamp, 7309: operation key, 7310: connection terminal, 7311:        sensor, 7312: microphone, 7400: mobile phone, 7401: housing,        7402: display portion, 7403: operation button, 7404: external        connection port, 7405: speaker, 7406: microphone, 8001: lighting        device, 8002: lighting device, 8003: lighting device, and 8004:        lighting device

This application is based on Japanese Patent Application serial no.2011-102554 filed with Japan Patent Office on Apr. 29, 2011, the entirecontents of which are hereby incorporated by reference.

The invention claimed is:
 1. An organometallic complex having astructure represented by Formula (G1),

wherein: R¹ represents any of an unsubstituted alkyl group having 1 to 4carbon atoms, a substituted or unsubstituted phenyl group, and anunsubstituted naphthyl group; R² represents hydrogen or an unsubstitutedalkyl group having 1 to 4 carbon atoms; Ar¹ represents a substituted orunsubstituted 1,2-phenylene group, an unsubstituted 1,2-naphthalene-diylgroup, or an unsubstituted 2,3-naphthalene-diyl group; and M representsiridium (Ir).
 2. The organometallic complex according to claim 1,wherein: the organometallic complex is represented by Formula (G2);

R³ to R⁶ separately represent any of hydrogen, an unsubstituted alkylgroup having 1 to 4 carbon atoms, an unsubstituted alkoxy group having 1to 4 carbon atoms, an unsubstituted alkylthio group having 1 to 4 carbonatoms, a halogen group, an unsubstituted haloalkyl group having 1 to 4carbon atoms, a substituted or unsubstituted phenyl group, and anunsubstituted naphthyl group.
 3. An organometallic complex representedby Formula (G3),

wherein: L represents a monoanionic ligand; R¹ represents any of anunsubstituted alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted phenyl group, and an unsubstituted naphthyl group; R²represents hydrogen or an unsubstituted alkyl group having 1 to 4 carbonatoms; Ar¹ represents a substituted or unsubstituted 1,2-phenylenegroup, an unsubstituted 1,2-naphthalene-diyl group, or an unsubstituted2,3-naphthalene-diyl group; M represents iridium (Ir); n represents 2,and the monoanionic ligand is any of a monoanionic bidentate chelateligand having a beta-diketone structure, a monoanionic bidentate chelateligand having a carboxyl group, a monoanionic bidentate chelate ligandhaving a phenolic hydroxyl group, and a monoanionic bidentate chelateligand in which two ligand elements are both nitrogen.
 4. Theorganometallic complex according to claim 3, wherein: the monoanionicligand is represented by any of Formulae (L1) to (L6);

R¹¹ to R⁴² separately represent any of hydrogen, an unsubstituted alkylgroup having 1 to 4 carbon atoms, a halogen group, a vinyl group, anunsubstituted haloalkyl group having 1 to 4 carbon atoms, anunsubstituted alkoxy group having 1 to 4 carbon atoms, and anunsubstituted alkylthio group having 1 to 4 carbon atoms; and A¹ to A³separately represent any of nitrogen, sp² hybridized carbon bonded tohydrogen, and sp² hybridized carbon bonded to any of an alkyl grouphaving 1 to 4 carbon atoms, a halogen group, a haloalkyl group having 1to 4 carbon atoms, and a phenyl group.
 5. The organometallic complexaccording to claim 3, wherein: the organometallic complex is representedby Formula (G4);

R³ to R⁶ separately represent any of hydrogen, an unsubstituted alkylgroup having 1 to 4 carbon atoms, an unsubstituted alkoxy group having 1to 4 carbon atoms, an unsubstituted alkylthio group having 1 to 4 carbonatoms, a halogen group, an unsubstituted haloalkyl group having 1 to 4carbon atoms, a substituted or unsubstituted phenyl group, and anunsubstituted naphthyl group.
 6. The organometallic complex according toclaim 5, wherein: the monoanionic ligand is represented by any ofFormulae (L1) to (L6);

R¹¹ to R⁴² separately represent any of hydrogen, an unsubstituted alkylgroup having 1 to 4 carbon atoms, a halogen group, a vinyl group, anunsubstituted haloalkyl group having 1 to 4 carbon atoms, anunsubstituted alkoxy group having 1 to 4 carbon atoms, and anunsubstituted alkylthio group having 1 to 4 carbon atoms; and A¹ to A³separately represent any of nitrogen, sp² hybridized carbon bonded tohydrogen, and sp² hybridized carbon bonded to any of an alkyl grouphaving 1 to 4 carbon atoms, a halogen group, a haloalkyl group having 1to 4 carbon atoms, and a phenyl group.
 7. An organometallic complexrepresented by Formula (G5),

wherein: R¹ represents any of an unsubstituted alkyl group having 1 to 4carbon atoms, a substituted or unsubstituted phenyl group, and anunsubstituted naphthyl group; R² represents hydrogen or an unsubstitutedalkyl group having 1 to 4 carbon atoms; Ar¹ represents an unsubstitutedarylene group having 6 to 10 carbon atoms; M represents iridium (Ir);and n represents
 3. 8. The organometallic complex according to claim 7,wherein: the organometallic complex is represented by Formula (G6);

R³ to R⁶ separately represent any of hydrogen, an unsubstituted alkylgroup having 1 to 4 carbon atoms, an unsubstituted alkoxy group having 1to 4 carbon atoms, an unsubstituted alkylthio group having 1 to 4 carbonatoms, a halogen group, an unsubstituted haloalkyl group having 1 to 4carbon atoms, a substituted or unsubstituted phenyl group, and anunsubstituted naphthyl group.
 9. The organometallic complex according toclaim 3, wherein the organometallic complex is represented by Formula(100),


10. The organometallic complex according to claim 3, wherein theorganometallic complex is represented by any of Formulae (112), (113),(132), and (133)


11. The organometallic complex according to claim 1, wherein, in thecase where the phenyl group and the 1,2-phenylene group havesubstituent, the phenyl group and the 1,2-phenylene group are separatelysubstituted by one or more alkyl groups each having 1 to 4 carbon atoms,one or more alkoxy groups each having 1 to 4 carbon atoms, one or morealkylthio groups each having 1 to 4 carbon atoms, one or more arylgroups each having 6 to 10 carbon atoms, one or more halogen groups, orone or more haloalkyl groups each having 1 to 4 carbon atoms.
 12. Theorganometallic complex according to claim 2, wherein, in the case wherethe phenyl group has substituent, the phenyl group is substituted by oneor more alkyl groups each having 1 to 4 carbon atoms, one or more alkoxygroups each having 1 to 4 carbon atoms, one or more alkylthio groupseach having 1 to 4 carbon atoms, one or more aryl groups each having 6to 10 carbon atoms, one or more halogen groups, or one or more haloalkylgroups each having 1 to 4 carbon atoms.
 13. The organometallic complexaccording to claim 3, wherein, in the case where the phenyl group andthe 1,2-phenylene group have substituent, the phenyl group and the1,2-phenylene group are separately substituted by one or more alkylgroups each having 1 to 4 carbon atoms, one or more alkoxy groups eachhaving 1 to 4 carbon atoms, one or more alkylthio groups each having 1to 4 carbon atoms, one or more aryl groups each having 6 to 10 carbonatoms, one or more halogen groups, or one or more haloalkyl groups eachhaving 1 to 4 carbon atoms.
 14. The organometallic complex according toclaim 3, wherein Ar¹ represents any of the unsubstituted 1,2-phenylenegroup, the unsubstituted 1,2-naphthalene-diyl group, and theunsubstituted 2,3-naphthalene-diyl group.
 15. The organometallic complexaccording to claim 3, R¹ represents any of the unsubstituted alkyl grouphaving 1 to 4 carbon atoms, the unsubstituted phenyl group, and theunsubstituted naphthyl group, and wherein Ar¹ represents any one of theunsubstituted 1,2-phenylene group, the unsubstituted1,2-naphthalene-diyl group, and the unsubstituted 2,3-naphthalene-diylgroup.
 16. The organometallic complex according to claim 5, wherein, inthe case where the phenyl group has substituent, the phenyl group issubstituted by one or more alkyl groups each having 1 to 4 carbon atoms,one or more alkoxy groups each having 1 to 4 carbon atoms, one or morealkylthio groups each having 1 to 4 carbon atoms, one or more arylgroups each having 6 to 10 carbon atoms, one or more halogen groups, orone or more haloalkyl groups each having 1 to 4 carbon atoms.
 17. Theorganometallic complex according to claim 5, wherein R³ to R⁶ separatelyrepresent any of hydrogen, an unsubstituted alkyl group having 1 to 4carbon atoms, an unsubstituted alkoxy group having 1 to 4 carbon atoms,an unsubstituted alkylthio group having 1 to 4 carbon atoms, a halogengroup, an unsubstituted haloalkyl group having 1 to 4 carbon atoms, anunsubstituted phenyl group, and an unsubstituted naphthyl group.
 18. Theorganometallic complex according to claim 7, wherein, in the case wherethe phenyl group and the 1,2-phenylene group have substituent, thephenyl group and the 1,2-phenylene group are separately substituted byone or more alkyl groups each having 1 to 4 carbon atoms, one or morealkoxy groups each having 1 to 4 carbon atoms, one or more alkylthiogroups each having 1 to 4 carbon atoms, one or more aryl groups eachhaving 6 to 10 carbon atoms, one or more halogen groups, or one or morehaloalkyl groups each having 1 to 4 carbon atoms.
 19. The organometalliccomplex according to claim 8, wherein, in the case where the phenylgroup has substituent, the phenyl group is substituted by one or morealkyl groups each having 1 to 4 carbon atoms, one or more alkoxy groupseach having 1 to 4 carbon atoms, one or more alkylthio groups eachhaving 1 to 4 carbon atoms, one or more aryl groups each having 6 to 10carbon atoms, one or more halogen groups, or one or more haloalkylgroups each having 1 to 4 carbon atoms.